interim guide on identifying prioritising and treating hazardous locations on roads in malaysia -...

Roads BranchPublic Works Department Malaysia

Jalan Sultan Salahuddin50582 Kuala Lumpur

JKR 20708-0022-95

Interim Guide On

Identifing, Prioritising And

Treating Hazardous

Locations On Roads

In Malaysia5.0m5.0m

7.0m7.0m

FOR INTERNAL USE ONLY

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Interim Guide On Identifying, Priortising And TreatingHazardous Locations On Roads In Malaysia

Cawangan Jalan, Ibu Pejabat JKR, K.L

FOREWORDRoad accidents have now become a major concern in Malaysia. The latest accident figures fromthe Royal Malaysia Police show that the numbers have increased by 23% and 15% over the lasttwo years alone, with 135,995 cases recorded for 1993. Malaysia's rapid economic growth may bepartly responsible for this worrying trend as the country is currently seeing registered vehiclesincrease by over 7 % per year. In order to sustain high rates of economic growth, utilisation of theskills of our people is of paramount importance, and the nation can ill afford to waste suchvaluable resources in road accidents. Many would argue that to minimise human suffering in anyway possible is sufficient justification in itself to devote greater efforts to reducing the roadaccident casualty toll.

Realising this, the Government set a reduction target in 1991 to reduce road accident fatalities by30 per cent by the year 2000 with 1989 chosen as the base year. To achieve this target, all relevantGovernment Departments and Agencies need to contribute to this effort. The approach to be takenfollows the 3 E's concept: Engineering, Education and Enforcement. Jabatan Kerja Raya (JKR)being the main Engineering arm of the Government can play a major role in this respect.

In line with this, Institut Kerja Raya Malaysia (IKRAM) has undertaken a road safety researchprogramme in collaboration with the Transport Research Laboratory (TRL) of the Unite Kingdom.As part of this initiative, IKRAM is now able to provide a reference guide for use by all practisingroad engineers in Malaysia. I am very pleased to be able to introduce this document, entitledInterim Guide on Identifying, Prioritising and Treating Hazardous Locations on Roads in Malaysiaand am grateful to the Overseas Development Administration, U.K. for their contribution to thefunding of this project.

This interim guide provides information specifically for Malaysia and sets out a standardmethodology for analysing accident data to help identify the most hazardous locations, selectappropriate remedial measures, and evaluate this action. It is my hope that this Guide will beuseful to all who are involved in the road safety field, helping them to channel limited resources ina more efficient manner, and thereby ensuring that our road network is as safe as it can possibly bemade.

(Tan Sri Dato’ Ir Wan A Rahman Yaacob)Director General of Public WorksJabatan Kerja Raya Malaysia 1995



Page 2Cawangan Jalan, Ibu Pejabat JKR, K.L

ACKNOWLEDGEMENTSThis Guide has been prepared within the Road Safety Group of the Institut Kerja RayaMalaysia (IKRAM) in association with the Transport Research Laboratory (TRL), UnitedKingdom. The author of the Guide is:

Mr. Chris Baguley - TRL.

As its intended users are all road authority engineers in Malaysia, the Guide was reviewed atvarious stages of its production by the following representative Committee:Ir. Mohamed Shafii Mustafa - IKRAM -Chairman Pn. Subiah Sulaiman - IKRAM -Secretary Pn. Norliah Saidin - Highway Planning Unit, Min.of Pub WorksAss. Prof. Radin U R Sohadi - Universiti Pertanian MalaysiaP/PPP Ruslan b. Khalid - Polis Di Raja Malaysia PPP Ooi In Boo - Polis Di Raja Malaysia Ir. Sabudin Mohd Salleh - Dewan Bandaraya Kuala LumpurEn. Sanusi b. Ismail - Jabatan Kerja Raya Daerah, Hulu Langat andrepresentatives from Jabatan Perumahan & Kerajaan Tempatan; Majlis Keselamatan JalanRaya; and Cawangan Jalan, Jabatan Kerja Raya.

The author is indebted to the above committee members for their valuable contributions, andto En. Othman Hussin of IKRAM for his assistance in preparing some of the material.Gratitude is also extended to Doncaster Metropolitan Borough Council and BerkshireCounty Council/Babtie Group for permission to reproduce parts of their Road Safety Plans,and to the Royal Society for the Prevention of Accidents (UK) for various extracts from theirRoad Safety Engineering Manual.

Finally, the author would also like to express his gratitude to the Director General of PublicWorks Malaysia for his permission to publish the Guide.


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1.1 PURPOSE AND SCOPEThis Guide is intended for use by trafficengineers and road safety officers in the PublicWorks Department (JKR), Ministry ofTransport (MoT), and all Local Authorities ofMalaysia.

It has been estimated that about 350,000 peopledie in road accidents in developing countrieseach year. This represents 70 per cent of thosekilled on the roads throughout the world. InMalaysia there are about 4,500 fatalities andover 36,500 injured per year. This means thatmore than 1 person in every 450 of the countrywill suffer injury or death in a road accidenteach year.

This situation is worsening, and traditionallythe "three E's" have invariably been quotedwhen discussing ways of tackling theproblem namely

Education,Enforcement and

EngineeringA fourth "E", Encouragement (by settingtargets, support for initiatives, publicitymaterial to promote positive attitudes, etc) hasnow also been added.

Although the most effective approachfor many road safety initiatives will be acombination of these elements, it is theEngineering approaches on which this Guide isfocused. It is likely that some aspect ofhighway design, layout, state of road or trafficcontrol is a contributory factor in most accidentoccurrence. It is well established thatconsiderable safety benefits may result fromthe application of appropriate road engineeringor traffic management measures at hazardousroad locations. In order to reduce accidentseffectively and help to achieve the nationallyset reduction targets, it is essential that asystematic approach to the identification ofhazards and selection of appropriate treatmentsbe carried out at the local level throughout the

country.

This Guide is designed to be an easyto-assimilate outline of procedures that have beenfound to be effective in many countries of theworld. It is hoped that this is achieved in asconcise a manner as possible, and it is thereforerecommended that for more in-depthdiscussions of the various topics the readershould make use of the References listed.

Indeed the Guide has been based on several ofthese publications, particularly the IndonesianAccident Investigation Procedures Manual, theInstitution of Highways and Transportation(UK) Guidelines for Accident Reduction andPrevention2, UK Department of Transport'sAccident Investigation Manual3, and RoSPARoad Safety Engineering Manual4.

1:1.1 Summary of contentsChapter I as an introduction, highlights thescale of the accident problem of Malaysia andintroduces the types of strategies generallyapplied in many other countries to reduceaccidents. The national accident reductiontarget is quoted and the need to manage roadsafety stressed.

Chapter II is devoted to the accident databaseof Malaysia, its production, and theresponsibilities of all those agenciescontributing to its content.

The third and subsequent chapters include astep-by-step approach (totalling 10 steps) totackling the safety problems within a roadauthority's area. These steps are illustrated inthe flow chart shown in Fig. 1.1.

The three steps of Chapter III comprise theinvestigation process. A list of the worstblackspot sites needs to be produced first fromthe computerised database. Preliminaryanalysis is described and early initial site visitsare also recommended.

CHAPTER IINTRODUCTION



Chapter IV (Steps 4 and 5) deals withdiagnosis of the problems, including thecollection of sketch diagrams and otheravailable data together with the likely needto carry out specific site studies. Detectingaccident patterns (a skill to be acquired) isintroduced.

The two steps (6 and 7) of Chapter V areconcerned with the selection of possiblecountermeasures and prioritising both theseand the sites to be treated. Lists of the mostcommon problems and treatments areincluded. A method of carrying out cost-benefit estimates to assist in the decision-making process for the most effectivemeasures is also described.

Chapter VI discusses the implementationstage (Step 8), that is detailed design andinstallation, briefly, and emphasises the needfor safety audits and for carrying out allroadworks as safely as possible.

The final two steps (9 and 10) in ChapterVII cover evaluation of the completedworks. Some observational measurementsfor monitoring the sites are described inbrief. Simple statistical techniques areoutlined to estimate the size of the effect ofthe measures introduced. All necessarystatistical tables are contained in theAppendices, as are examples of the PolicePOL27 accident report form and UK RoadSafety Plans (see 1:5.1).

1:2 WHAT IS A ROAD ACCIDENT?A full definition of a road traffic accident is:

"a rare, random, multi factor event alwayspreceded by a situation in which one ormore road users have failed to cope withtheir environment, resulting in a collision onthe public highway which should berecorded by the police".

Although, from the previous section, it maybe concluded that road accidents are far toocommon in Malaysia (see Section 1:5), theyare comparatively rare events at specific

points in the network. For example, even ata “high risk” junction in Malaysia having42,000 vehicles (16-hour count) passingthrough it and where 53 accidents occurredin one year with 10 involving injury, theactual accident occurrence rate is stillrelatively low. These accidents occurredduring about 18,300,000 vehiclemovements. That is, one damage-onlyaccident every 425,000 movements and oneinjury accident every 1,830,000 movements.

The precise moment when an accident willoccur can never be predicted, and even iflong periods such as a year are consideredthe numbers will fluctuate randomly about alonger term average. Statistical tests canshow whether, during one particular ‘high’year, a real change has occurred. Theoccurrence of accidents along the networktends to be less random as accidents areoften clustered at so-called "hazardouslocations" or "blackspots".

There is rarely an accident situation inwhich only one "thing" or person is truly thesole cause of the accident: hence accidentsare multi-factor events. There are three basiccategories of factors:

Road user errors




Road and environment faults

Vehicle defects

It has been shown that road user errors areby far the most prevalent factor but oftenanother factor(s) is present. For example,“adverse environment” implies a situationwhere a driver has had difficultymanoeuvring a vehicle safely; drivers arefrequently provided with insufficient orunclear information with respect to signsand markings; sometimes poor design cancause a driver to have a misleading visualimpression; and occasionally defective tyresand brakes can contribute significantly to anaccident occurring.

The chain of events leading up to anaccident include people’s experiences onthat day which can lead to stress or lack ofadequate concentration on the driving task,and ultimately mean that one or morepersons failed to cope with theirenvironment. An assessment of the factors inthe chain could indicate which road andenvironment factors may benefit from safetyengineering remedial measures.

Consider the example of a junction whereskidding on a wet road surface has beenrecorded in several accidents by the police.Care in analysis is needed as aninexperienced investigator may immediatelyrecommend that the skid resistance of roadsurfaces on the approaches to the junctionneed to be upgraded.

Careful study of the site (during similarconditions), however, may reveal that treebranches weighed down by rainwater tend toobscure road signs and advance warningsigns. The drivers thus failed to copeprimarily because of obscured signs ratherthan the wet road surface itself. Treating theroad surface may still be necessary butwould be much less effective if the treeswere not cut back or the signs not re-sitedfor improved visibility.

1:3 APPROACHES TO IMPROVINGROAD SAFETY

The main objective of improving road safetythrough road engineering and trafficmanagement simply means measures takenprimarily to avoid some accidents happeningin the future, or at the very least, reducingthe severity of future accidents.

This may be achieved by following two dis-tinct approaches:

(i) ACCIDENT PREVENTION (ii) ACCIDENT REDUCTION

ACCIDENT PREVENTIONInvolves the application of safety principlesin the planning, design, upgrading andmaintenance of roads. (See ref 5: The safetyaudit of highways).

ACCIDENT REDUCTIONInvolves the application of appropriate roadengineering or traffic management schemesat hazardous locations on the existing roadnetwork. Such applications, particularlythose of relatively low-cost, at known highaccident locations or “blackspot” haveyielded very high returns in many of themore industrialised countries of the world.

Although accident prevention plays anextremely important role in maintaining asafe environment, this Guide concentrateson accident reduction and is aimed atengineers and technicians who haveresponsibility for safety on the existing roadnetwork. It is recommended that for moreinformation about accident prevention thereader refer to ref.6: ‘Towards safer roads indeveloping countries - a guide for plannersand engineers’.

1:4 THE FOUR BASIC STRATEGIES

The four basic strategies for accidentreduction through the use ofcountermeasures are:




Single sites/Blackspotsthe treatment of specific types of accident ata single location[Eg. usually junctions, but could be areas200-400m in diameter, 300-500m stretchesof road]

Mass action schemesThe application of a remedy to locationswith a common accident problem.[Eg. skidding on wet road surface, head-oncollisions, excessive speed approachingroundabouts]

Route action plansThe application of remedies along a routewith a high accident rate.

Area-wide schemesThe application of various treatments over awide area of town/city.[Eg. including traffic management andtraffic calming (speed reducing devices) inareas bounded by links on a network,housing areas or l km squares having higheraccidents than a preset level].

Blackspot treatment is likely to be the most

effective and straightforward as a startingpoint, the road authority perhaps moving tothe other wider types of application as expe-rience is built up.

All these strategies rely on the availability ofdata which contains full information aboutaccidents and their locations so that commonfeatures which have contributed to theaccidents can be identified. Accident dataand the use of collision and stick diagrams,key analysis tools for the traffic engineer,are discussed in Chapters II and III.

1:5 SAFETY MANAGEMENTOne of the most effective initiatives inimproving safety has been found to be thesetting of realistic accident reduction targetsaround which all authorities can properlyplan reduction programmes.

In 1991 the Government of Malaysia set anational target:- to reduce the number offatalities resulting from road accidents by 30per cent by the year 2000. This was basedon the year 1989 which means, in practise, areduction from 3773 to 2641 deaths per year(fig. 1.3).




This was expressed by the special CabinetCommittee for Road Safety in 1990 in termsof a fatality rate reduction from 7.12 downto 3.14 deaths per 10,000 vehicles registeredto be achieved by the year 2000. Thesomewhat larger percentage reductionexpressed in the form of fatality rate is dueto the fact that this takes some account ofthe fairly substantial, steady increase invehicular traffic in Malaysia. Theassumption was that of continuing lineargrowth in the number of vehicles registeredas that experienced during the past ten years.(see fig. 1.4).

It can be seen from fig. 1.3 that there is agenerally increasing trend in deaths which isparticularly marked in more recent years.This disturbing feature makes it moreimportant than ever for all authorities towork hard to achieve their particular target.

Although aimed at fatalities, it is likely thatthe accident countermeasures employed willalso help to reduce the levels of severelyinjured casualties.

Safety management should allow the

national target (which needs to bedisaggregated into State and local targets) tobe reflected in safety initiatives for eachlocal area.

For example, Fig. 1.5, from the U.K.’sInstitution of Highways & Transportation’s(IHT) road safety guidelines, illustrates thelarge number of policy initiatives which canbe input into each local area scheme, ie. theintegrated approach where agencies need toco-operate in agreeing targets and plans, andneed to monitor the effects of the safetywork.

1:5.1 Road Safety PlansIt is recommended that each highwayauthority produces an annual Road SafetyPlan in which the local casualty reductiontarget is stated and a strategy for achievingthe targets is developed.

Sample contents of some annual Planspublished in the U.K. are included inAppendix A. Before producing such adocument, the following will be required:




Review of existing highways andtransportation policy

Investigation of accident trends forvarious road user groups in the authority’s geographical area

knowledge of the working structure of the authority (relationship between departments, committees external agencies concerned with safety).

The key to success lies in setting a series ofachievable casualty reduction targets (shortand long-term) that can be monitored, andbeing able to acquire the increased resourcesthat will inevitably be required.

The Plan should include:

Background to the road accident situation in the authority area (accident trends with respect to roaduser groups, road features etc)

Aims of the Plan (casualty reductiontargets)

Summary of proposals planned (including major capital schemes,smaller remedial engineering work,safety audit, maintenance, costs, relationships with other agencies, safety publicity, traffic law enforcement)

Methods for monitoring andevaluation

Report of previous year's work andeffect on accidents

The Plan should be a comprehensivedocument containing photpgraphs, graphsand figures and should be made available tothe public.





REFERENCES

1. TRANSPORT AND ROAD RESEARCH LABORATORY. Interim manual on accident investigation procedures and the development of low-cost engineeringimprovement schemes. TRRL, Pusat Litbang Jalan, Ministry of Public Works Indonesia, Jalan Raya Timur No. 264, Bandung - 1993.

2. INSTITUTION OF HIGHWAYS AND TRANSPORTATION. Highway safetyguidelines: accident reduction and prevention. International edition. IHT, 3 LygonPlace, Ebury Street, SWIW OJS, London - 1990.

3. DEPARTMENT OF TRANSPORT. Accident Investigation Manual. Royal Society for the Prevention of Accidents, Cannon House, The Priory Queensway, B4 6BS,Birmingham - 1986.

4. ROYAL SOCIETY FOR THE PREVENTION OF ACCIDENTS. Road safetyengineering manual. RoSPA, Cannon House, The Priory Queensway, B4 6BS,Birmingham - 1992.

5. INSTITUTION OF HIGHWAYS AND TRANSPORTATION. Guidelines for: thesafety audit of highways. IHT, 3 Lygon Place, Ebury Street, SWlW OJS, London- 1990.

6. TRANSPORT & ROAD RESEARCH LABORATORY. Towards safer roads in developing countries: a guide for planners and engineers. TRRL & Oversea’sDevelopment Admin., Old Wokingham Road, RG11 6AU, Crowthorne - 1991.



2.0 INTRODUCTIONAn essential element of any accidentreduction and prevention strategy is thecollection and investigation of road accidentdata. Accident investigation procedures inthe context of this Guide depend on theexistence of a reliable database.

This chapter outlines the database which isnow being established in Malaysia with themicrocomputer system that can be used foranalysing this data.

2:1 PRODUCTION OF THE ACCIDENT DATABASE

All accident data originates with therecording of details by the police either atthe scene of an accident or as subsequentlyreported to them at the local police stationby those involved. There will inevitably be asubstantial number of road accidents that arenot reported to the police at all.

The accident details are first recorded in thepolice officer’s notebook and a simplerecord is made in the 24-hour incident bookat the police station in which a uniquereference number is assigned to the accident.If human injury has occurred and/or aprosecution is likely, an accidentinvestigation file is opened, again having areference number. This contains alldocuments associated with the accident, eg.witness statements, photographs, descriptionand sketch diagram of the scene as found bythe police reporting officer. This file isrequired in the law courts in the event of aprosecution.

The traffic accident report form, POL27(Pin. 1/91), is a pre-printed standard formand is the basis of all computerised data. Itis also completed by the police accidentreporting officer.

The form comprises 15 pages, though

several pages are repeated (for reasons givenbelow): see copy of the form included inAppendix B.

The first page contains some brief generalinstructions on filling in the form, thoughfull instructions are contained in a separatebooklet (Panduan Mengisi Borang POL271).Data entry begins on page 2 which includesinformation of a general nature, such as thepolice station, accident reference number,time and date of the accident, number ofvehicles and casualties, road type andcondition, road geometry, collision type,weather and lighting conditions, etc.

This page also contains a small section forinformation on the closest kilometre post tothe accident. This important page of thePOL27 form is repeated twice (on pages 3 &4) such that carbon paper can be inserted toproduce copies for the Police District andalso the local JKR office or localgovernment department (see Section 2:3).

The second main page (page no. 5) providesspace for details of the vehicles involved inthe accident including their type, modelregistration number, damage suffered,defects, and their movement prior to thecollision. The details of the vehicle’s driveror rider are also included on this page. Theseinclude his or her age, sex, licence, injury(if any), whether any driving errors weremade and whether they were wearing a seatbelt or crash helmet.

This page of the form is repeated for up tothree vehicles involved in the accident withan additional carbon copy of each for thePolice District. If more than three vehiclesare involved then the reporting officersimply needs to attach additional pages, asnecessary. The next new page (page 11)deals with any passengers or pedestriansinvolved in the accident, where again


CHAPTER IIACCIDENT DATA



simple details such as age, sex, severity ofinjury, are recorded. The remainder of thispage contains estimates of the cost ofdamage to vehicles and/or property, and alsocodings for the location of the accident(see Section 2:2). Space for up to twelveinjured passengers and six pedestrians isincluded on this page, where a carbon copyis again provided for Police Headquarters.

The final page (page 13) includes a shortspace for the reporting officer to describehow the accident happened. Another box isprovided for a sketch of the accidentincluding the position of the vehicles priorto the collision, and the collision point inrelation to the road layout. Separate space isprovided for a location sketch where asimple map should be drawn showingclearly where the accident occurred on theroad network.

Two carbon copies of this last page areprovided for both the Police District and thelocal JKR District Office or LocalGovernment Department. The original/topcopy of the form is sent to PoliceHeadquarters in Kuala Lumpur.

2:2 LOCATION CODINGLocation coding is a very important featureof the accident data as it provides the onlyway in which an engineer can obtain a truepicture of where his safety problems exist.Two methods of location coding have beenadopted in Malaysia and these are:

1. Network coding2. Grid coordinate coding

The function of the Network coding is toprovide a means of examining easily andreliably a particular route or junction, orlisting those with the worst accident records.The Grid coordinate coding provides anabsolute location reference and means ofplotting accident maps (essential forGeographic Information Systems).

As well as facilitating both analysis feature,

recording the coding for both systems foreach accident also serves as a cross-checkon the accident location (it has been foundelsewhere that errors are often made in therecording of grid coordinates).

Roads in Malaysia are one of fivecategories: -i) Expressway (Toll) ii) Federaliii) State iv) Urban v) Other (District Council or private)

2:2.1 Rural AreasFor rural roads (types i,ii,iii or v above),kilometre posts should be used as thenetwork coding system. The Police reportingofficer should estimate the position of theaccident (to the nearest 100m) from theclosest kilometre post. On Expressways thistask is made easier as 100m posts have alsobeen installed.

The national grid coordinate system shouldbe included on all maps used such that theposition of the accident can be read offeasily.

2:2.2 Urban AreasFor urban areas (types iv or v above), aNode system needs to be devised whereeach major road junction is given a uniquenumber (for that particular map).

Sections of road between junctions areknown as Links and can be uniquely definedby the node numbers on each side of theaccident.

Where an accident occurs off the main roadnetwork the location can be approximatelydefined by a unique Cell number. Cellnumbers are simply areas containing smallerroads (eg. housing areas) which arenormally bounded by the main road net-work, and should be assigned a differentnumerical sequence (eg. 900-999).

Again, the national grid coordinates must




also be recorded by reading off values onthe appropriate map.

2:3 RESPONSIBILITIES WITHRESPECT TO ACCIDENT DATA

The production of the accident database forMalaysia is shown diagrammatically in Fig.2.1. and the responsibilities of variousauthorities are outlined in the followingsections.

2:3.1 PoliceAs mentioned above, when the local policestation has completed a POL27 formaccording to their coding instructions1, thetop copy is sent to the Police District Office,where it is checked, and then sent on toPolice Headquarters at Bukit Aman, KualaLumpur. In practise, this tends to be done inbatches, normally each week. At the sametime pages 4 and 15 of the form are sent outto either the local JKR District Office or theLocal Government Office, as appropriate.

The forms are further checked forcompleteness at Bukit Aman and thenprocessed (with other crime records) forentry onto the mainframe computer. At theend of each month, the accident file isdownloaded to a microcomputer diskette andthe data-file converted into the TransportResearch Laboratory's MicrocomputerAccident Analysis Package2 (MAAP), whichhas now been adopted as the standardaccident analysis tool for Malaysia.

2:3.2 JKRThe responsibility for precise locationcoding for each accident now lies with thevarious road authorities, as this is of primaryimportance to them. This is why copies ofpages 2 and 13 (ie. pages 4 & 15 containingroad number, kilometre post and collisionsketches) of each accident are eitherdelivered to or collected from the JKRDistrict Office or Local Government Officesfor completion of the relevant sections.

The appropriate officers at the JKR DistrictOffice are required to check location details

of each accident and complete the coding of:

Route number

Lowest Section number of km postson either side of accident

Nearest 100m from the above post

Relevant map code and series

X-coordinate (easting)

Y-coordinate (northing)

Direction in which vehicle at faultwas travelling

In order to provide this data the JKR Officewill first need to acquire 1:25000 scaletopographical maps of their area. Ideallywith the use of a calibrated measuring wheelattached to a car, all State and Federal roadsin the area need to be driven along slowlyand logged; ie. the position of kilometreposts and other landmarks in relation toreference points already marked on the map(eg. road junctions) are noted as accuratelyas possible. On average, a feature orpermanent land-mark should be noted atleast every 1/4km.

This information can then be transferred tothe maps: an example of part of such a mapis given in Fig. 2.2. If not already shown,one kilometre squares also need to beaccurately drawn on the maps correspondingto the position of the national gridcoordinates.

With the additional landmark informationand using the Police descriptions andlocation sketch on the POL27 form, itshould now be possible for the JKR engineerto pinpoint accidents much more easily onthe appropriate map, and thus fill in theaforementioned location data.




At the 1:25000 scale, it should just bepossible to record the X and Y coordinatesfor each accident location to the nearest 10m(though the error may be ±25m).

All completed forms should be sent to theHighway Planning Unit (HPU) of theMinistry of Works in Kuala Lumpur everymonth.

2:3.3 Local GovernmentFor towns or cities it has been found to bemore practical to use a node system. TheLocal Government Department are thusrequired to complete the followinginformation on the POL27 forms sent tothem:

Route number (where one exists)

Relevant map code and series

X-coordinate (easting)

Y-coordinate (northing)

Node number of accident or nearestnode (if not at junction) or cell

Node number on other side of accident (if not at junction)

Direction in which vehicle at faultwas travelling

Again this requires the production of specialmaps, in this case producing a standard nodesystem. For town/city maps a scale of1:5000 (or at most 1:10000) isrecommended. The Local GovernmentDepartment should then assign a uniquenode numbering system preferably to alljunctions in the' city. An example of part ofsuch a node map is shown in Fig. 2.3.

Again, if not already shown, squarescorresponding to the national grid should beaccurately drawn on the maps. (preferably100m grid squares). This will enable X-Ycoordinates to be noted easily to an accuracyof 10m.

All completed forms should again be sent toHPU on a monthly basis




2:3.4 Ministry Of Public WorksOn receipt of the completed parts of theforms (pages 4 and 15) the locationinformation is further checked by HPU andentered with the accident identifyingparameters onto computer.

This will eventually be merged (once permonth) with the corresponding accidentrecords received from the Police (see Fig.2.1). In theory, the database is now completeand can be sent out in the form of relevantMAAP data files for use by the roadauthorities or analysis by other interestedgroups.

2:4 RESOURCES REQUIREDIn order to be successful in not onlymaintaining the accident database butachieving the local casualty reductiontargets, resources will be required for bothcapital expenditure and staff time.

Both the Institution of Highways andTransportation (IHT)3 and Local AuthorityAssociations4 in the UK stronglyrecommend that a local road authorityshould establish a specific AccidentInvestigation Unit for this data maintenance,analysis and engineering side of accidentreduction and prevention. The advantage ofsuch a group is that it can dedicate its timeto the task and not be diverted onto othertraffic or highway matters.

The IHT Guidelines suggest a staffing levelof one engineer or technician for each 400-1000 reported accidents per year, dependingon whether the Unit can pass detailed designand implementation of schemes to anothersection. The staff must be trained as safetyengineering is a specialised area of work.

Adequate capital resources are also requiredin order to implement the extensive remedialwork necessary to meet the local targets. Itis therefore recommended that a set amountbe specified in each annual budget of theroad authority which is reserved solely forsafety expenditure (maintaining the database

and safety improvements).

For larger scale safety improvements it isrecommended that central governmentprovide a Special Road Safety Fund fromwhich road authorities can apply for grantssupplementary to their annual budget. Theapplication will, of course, need to bejustified for each scheme in terms ofexpected accident reductions which willcontribute to achieving the local target.





REFERENCES

1. POLIS DI RAYA MALAYSIA. POLIS 27 (Pindaan 1/91) - Panduan Mengisi Borang. Cawangan Trafik, Ibu Pejabat Bukit Aman, Kuala Lumpur - 1991.

2. HILLS, B L, G J ELLIOTT & D CLARKE. Microcomputer Accident AnalysisPackage v5.0 (MAAPfive) User guide. Transport Research Laboratory, Overseas Centre, Crowthorne - 1994.

3. INSTITUTION OF HIGHWAYS AND TRANSPORTATION. Highway safety guidelines: accident reduction and prevention. International edition. IHT, 3 LygonPlace, Ebury Street, SWIW OJS, London - 1990.

4. LOCAL AUTHORITY ASSOCIATIONS. Road safety code of good practice. C/oHertfordshire County Council, Highways Dept, North Road, Hertford, SG14 2PY,U.K. - 1989.



3:0 INTRODUCTIONThe following chapters contain a stepby-stepapproach to tackling the problem ofhazardous locations on a regular basis.

The main objective of this engineeringsafety work is to change the roadenvironment in the most efficient manner(ie. within a specified budget) such that themaximum benefit in terms of accidentsavings is gained. This chapter is concernedwith finding out where problem locationsexist and the preliminary investigationrequired to try to determine the nature of thesafety problems.

Step 1: Identifying And PrioritisingSites

3:1. ACCIDENT DATA SEARCHIt is necessary to identify high accident sitesin the network for which the road authorityhas responsibility. Ideally, a period of 3 to 5years of accident data should be reviewed.This is because accidents, even at veryhazardous locations, are relatively rareevents having a considerable randomelement, particularly in the time at whichthey occur. Statisticians tend to agree,therefore, that as a general rule, three yearsis really the minimum period needed tosmooth out any abnormally large randomfluctuations, to produce a reliable ranking ofhazardous sites, and eventually to makeevaluations of the treatments (ie. comparewith a 3-year ‘after’ period).

However, if such a long period is not yetavailable on the local computer database,rather than wait for this time to elapse,shorter periods can be investigated as longas caution is exercised over the conclusionsmade.

This Guide assumes that a microcomputer,the MAAP software (see 2:3.1), and relevantdatasets are available to the investigator

3:1.1 Ranking blackspot sites

The first stage is to study the data in alogical manner to rank problem sites. It isimportant to note at this stage that the initiallisting will need to be modified to produceone of ‘treatable’ sites. For example,consider Fig. 3.1 (a) and (b) summarisingaccident data types for two roundabout siteswith similar accident numbers. In (a) thereare a large number of similar accidentsinvolving loss of control or skidding duringthe hours of darkness. This may well betreatable by improved skid resistant surfaceor drainage, improved signing and lighting.However, at site (b) there is no obviousdominant pattern; thus only site (a) cantherefore be classed as a treatable site.It important to try to define a “reactionlevel” * , ie. the number of accidents orpoints above which the investigator takessome action. The reaction level is set basedon the following three variables:

Number of accidents: a) all injury accidentsb) severity points weightingc) all pedestrian injury accidents

Type of highway unit:a) kilometre lengthb) within 50m of junctionc) links or mid-block accidents d) all roads in a defined area

Time period:a) 12-month periods of consecutive

months, (not necessarily a calendaryear) are the normal periods used.


CHAPTER IIIINVESTIGATION

*The Highway Planning Unit's current accident points weighting system is accidents involvingfatality= 6 serious injury = 3

slight injury = 0.8 damage-only = 0.2



An example of a reaction level criterioncould be a blacksite definition of:

9 or more injury accidents,[or 15 points or more],

within 50m of a junction, [or on a 200m road section],

over the past 3 years.

It is probably better to focus on injuryaccidents in setting a reaction level as thesetend to be more reliably reported thandamage-only ones. The following sectionsexplain how sites can be ranked according tothe four approaches to accident reductionmentioned in Chapter 1.

3:1.1.1 Route action sitesThe simplest way of ranking sites, and theone currently recommended for use inMalaysia, is to list them in descending orderof accident totals for either sections of road,nodes, or grid referenced cells. Highwayauthorities elsewhere sometimes useaccident rates but these necessitate trafficflow counts to be available at all points onthe network, and also tend to give lowerrankings to the high-flow, high-accidentwhere potentially more accidents could besaved.

To produce a list using MAAP, select theLocation option from the main menu bar andselect Kilometre & Link/Node analysis. If aparticularrural road is being studied, selecteither the 1km or 100m analysis option, andthen set any Conditions, such as, to includeonly those accidents involving personalinjury accidents.

An example of a kilometre plot of accidentsfor a 27km stretch of Federal Route 1 over aperiod of three years is shown in Fig. 3.2(using the Zoom option to specify lkmlengths). A list of the worst 100m sections ofthis stretch is shown in Fig.3.3 (using theWorst button which will prompt for thenumber of sites to include in the analysis).With reference to Fig. 3.2 it can be seen thatthe worst kilometres are:

417 (includes 2 fatal accidents) 419422 415 420409 (includes 1 fatal accident).

If the reaction level for this particular roadauthority was set at 9 injury accidents in a100m section in 3 years (ie. as in Fig. 3.3),the first 7 locations are included in theabove list (Table 3.1), though in a slightlydifferent ranking order.

Taking this a step further, if the severity ofaccidents is further taken into account byweighting factors (which are normallyrelated to the average accident cost of eachseverity level), and damage-only accidentsare also included (having a real cost), thisresults in the ranking shown in Table 3.1.

It can be seen that in this particular case,which considers a small 27km length ofroad, the same seven sites appear at the topof the list irrespective of the ranking methodused. However, the priority order variessomewhat, and is likely to change againwhen more indepth investigation is carriedout to determine treatable sites.

3:1.1.2 Single sitesThe priority listing for single sites in a townor city can be handled in much the sameway as in the previous section once a nodenumbering system has been established anddata entered onto computer.

For a particular town, MAAP can produce alist of the worst nodes or links (mid-blockaccidents between adjacent nodes) as in theexample shown in Fig. 3.4.

To produce such a list, select the Locationoption from the main menu bar and selectKilometre & Link/Node analysis as above.Now select Worst node. Set any Conditions,such as, to include only those accidentsinvolving personal injury accidents. FinallySelect data files to be included in the




analysis.

Once a pass has been made through the datafiles, the user will be prompted for thenumber of nodes to include in the list.

Again weighting factors can be applied tothe different severity levels to obtain acost-related ranking of sites.

3:1.1.3 Mass action sitesIn order to determine sites for mass actiontreatment it is necessary to relate a selectedtype of accident feature to individual sitesand to initially rank the latter according tothe numbers of accidents of the selectedfactor.

Some examples of these would be asfollows:

Locations with the worst records of: Accidents on bendsRight-turn accidents Overtaking accidents Nighttime accidentsPedestrians crossing road accidents Bicycle/motor-cycle accidents

It is often more difficult to rank mass actionsites because a particular accident typenormally only represents a sub-set of thedata at any one site. Thus smaller numbersare usually involved. However, the simplestapproach is to try to assess the likelyaccident saving for each mass action planand rank these, producing a list with thegreatest potential for accident savings at thetop of the list.

3:1.1.4 Area wide actionAs single blackspot sites are graduallytreated accident occurrence can be ratherscattered, and so attention generally tends toturn to wider areas, particularly urbanresidential areas. In urban areas in Malaysia,it is not uncommon for parts of towns tohave well over 100 accidents (and some-times over 50 injury accidents) per squarekilometre per year.

Again, ranking areas for treatment is not asimple matter and an assessment of thepotential accident savings for each actionplan should be made. Those yielding thebest returns in terms of accident savingsrelated to cost of implementation should be




made. Those yielding the best returns interms of accident savings related to cost ofimplementation should be placed at the topof the list.

MAAP can also be used to produce countsof accidents in grid squares or irregularlyshaped areas if a digitised or scanned map(to national grid coordinates) is availableand accident locations have also beenrecorded by coordinates on the database(see Fig. 3.5 example). It is probably best toinitially use MAAP to produce a grid squarecount and then consider, say, ten areas whichcould possibly each be treated as a package,that is, bounded by roads, railway lines,rivers or other geographic features.

This type of ranking is normally carried outby focusing on the vulnerable road users.For example, total accidents involving someor all of the following groups could be plot-ted:

All motorcycle riders all pedalcyclistsChild pedal cyclists (under 16 years)All pedestrian casualtiesChild pedestrians (under 16 years)

STEP 2: Preliminary Accident Analysis

3:2. REFINING THE RANKINGBY STATISTICALTECHNIQUES

Before embarking on an in-depthinvestigation at any site, it is advisable tocheck that the site has higher numbers ofaccidents than might be expected, and thatthis difference is statistically significant. Thefollowing sections outline some simplestatistical techniques which may be used.

3:2.1 Averages or "Norms"It is important to know whether the level ofaccidents is higher than expected, forexample, whether the number of skiddingaccidents at a site is worse than average.

If a particular route is under consideration,this can be divided up into equal lengths(eg. kilometres) and the average number ofaccidents per section calculated. This isreferred to as the arithmetic mean or norm.

To determine whether particular sectionswarrant further investigation, the standarddeviation (measure of the variability in thedata) is normally calculated. The coefficientof variation Cv is a simple measure of how aset of data varies from its mean, with valuesof Cv > 1 regarded as very substantialdeviation.




Those sites that have more accidents thanthe mean plus 1 standard deviationshould be the first to be singled out forinvestigation.

ExampleConsider the example stretch of FederalRoute 1 shown in Fig. 3.2 and take x as thefrequency of injury accidents in three years.

Thus there is considerable variation between1km sections along this road in theiraccident occurrence. Those sections withmore than 12 accidents (ie. 6.22 + 6.62) arecertainly worthy of further investigation, ie:

Section: 417 419422 419

3:2.2 The Poisson TestThis test (for randomly occurring events) iscommonly used to determine whether arecent increase in accidents at a site was dueto random fluctuation only (and will returnto previous levels).

It is used to calculate the probability of aparticular frequency of accidents occurringin a year when the long term average isknown.

ExampleLet us assume the injury accident figures fora site are as follows:

1991 = 2 accidents 1992 = 0 accidents 1993 = 1 accident1994 = 5 accidents

If this site is selected on the basis of the lastyear, it is better to confirm that some changehas happened at the site such that the nextyear will also be high, and not that theapparent increase has occurred by chance.

Long term average = (2+0+1+5)/4 =2

Using the Poisson Probability (Single factorvalues) tables given in Appendix C, look forthe high year value of 5 in the left handcolumn (k=5) and across to the column ofλ(mean) =2. The value here is 0.0361 whichmeans that the probability of 5 accidentsoccurring where the long term average is 2,is 0.0361 or 3.61 %.

However, the likelihood of 5 or moreaccidents occurring at the site should bequoted. To do this simply add theprobabilities of k=5, k=6, k=7, k=8 etc.

That is:0.0361 + 0.0120+ 0.0034+ 0.0009+ 0.0002

= 0.0526

Thus the probability of 5 or more accidentsoccurring due to random fluctuation is5.26%

ie. about a 1 in 20 chance that this is random,

or a 94.74% (100-5.26) chance that this is areal increase.




3:2.3 Chi Squared testThis test is normally used for two purposes:

To determine whether the number ofaccidents of a particular type is"significantly" higher than at similar sites

To check whether there has been a "significant" change in the number ofaccidents at a site after treatment hasbeen carried out.

ExampleA particular junction is suspected of havinga poor skid resistant road surface, and hasthe following accident record:

‘Skidding’ accidents = 7No skidding reported = 5

For all other similar junctions along thisroad the accident record over the sameperiod was:

‘Skidding’ accidents = 37No skidding reported = 178

We need to test whether the skiddingaccidents are significantly different fromwhat might be expected. The following(2x2) table should be set up:

In the Chi Squared Distribution Table(Appendix D), looking along the line withone degree of freedom (v=1), the value justbelow the 9.81 calculated above is 6.64which is the 0.01 “significance” level, ie.1%.

This means that the chance of getting 7skidding accidents at a site with a total of 12by chance is only 1 % (one in data isinterrogated. 100 chance). Thus it seemsfairly certain that there is some reason whythe skidding accidents are occurring at thissite

3:2.4 Interpretation of “significance”The significance or confidence levels ofresults from the above statistical tests can beinterpreted with the following practicalmeanings:


* N.B. The above formula allows for Yates' correction which overcomes the inaccuracies whichcould occur with the test when using whole numbers - as with accident frequencies. Also,note that the test becomes less reliable if any cell has a value less than S.



it is generally agreed that only resultssignificant at (or better than) the 5% levelcan be regarded as conclusive.

3:2.5 In-depth analysis - initial stageHaving now obtained a priority list of sitesfor investigation, it is advisable to produce a“working file” of accidents for each site.This can be done easily on MAAP andmeans that all subsequent analysis can becarried out of the working file, withouthaving to search the whole database eachtime the data is interrogated.

Use the Find Records option from the mainmenu bar and choose Find Selected Records.In this menu select Create Working file andthen Set Conditions to extract all accidentsfor the site under investigation.

The conditions to be set may be of the following types:

i) Kilometre (Section) No. also set: Road Number Nearest 100m

(if possible)ii) Node No.

also set: Map code or State andDistrict and PoliceStation No

iii) X-coordinate range and Y-coordinaterange

The working files should include asmany years data as available. Clear,meaningful names should be given to theseworking files so that they can be easily identified at a later date or by other users.

A stick diagram of each site can nowbe produced using these files. This isproduce a “working file” of accidents simplya way of displaying each accident record asa column of data. The purpose of the stickdiagram is toassist the investigator to lookquickly patterns of similar types of accidentfor which some appropriate engineeringsolution can be devised. The factorsleading to accidents will be dealt with inmore detail in Step 5, but at this

solution can be devised. The factors leadingto accidents will be dealt with in more detailin Step 5, but at this stage the stick diagramgives investigator a “feel” for the types ofaccidents occurring and provides anindication of what to look for during thepreliminary site visit.

Select Stick from the main menu bar and setany conditions if necessary. It is possible toset up a number of different stick formats ifrequired. An example of a stick diagram fromMAAP is given in Fig. 3.6, where eachaccident is represented symbolically by acolumn (or stick) of key information.

In this example, a T -junction (and one of theworst blackspots in Seremban), only injuryaccidents have been included; though itshould be noted that there were also 74damage-only accidents recorded in the 3year period. It can be seen immediately fromthe stick diagram that the injury accidents allincluded the vulnerable road users:motorcyclists and/or pedestrians.

Five of the six pedestrian casualties were infact struck by a motorcycle. Most of the othermotorcycle accidents (75 %) were sideimpacts or side swipes involving carsemerging from the side road and apparentlynot noticing or misjudging the motorcycle onthe main road. Only two of the 13 injuryaccidents were in darkness, thus poorlighting is unlikely to be a particular problemat this site.

The initial site visits should thereforeconcentrate on the turning manoeuvreproblem particularly with motorcyclists, andalso the pedestrian problem.




STEP 3: Initial Site Visit

3:3 PRELIMINARY VISITThe site visit is a very important element ofany accident investigation. The mainpurpose of the first site visit is to becomefamiliar with the site and to ensure thatavailable plans are up to date and detailedenough to identify specific features whichmay be contributing to accidents; forexample, visibility sight lines, street furni-ture, buildings.

The investigator should identify themanoeuvres indicated in the accident reportsand try to visualise the accidents,particularly those with commoncharacteristics. It might be necessary tomake visits at different times of the day, orin dark and/or wet conditions, in accordancewith the factors revealed in the stickdiagram.

It is often possible at this early stage tomake a preliminary assessment of the likelycauses of certain accident types.

The use of photographs taken atdriver/pedestrian eye height or an overallview can be an invaluable aid in the officeor at presentations to committees.

3:3.1 “Easy” & “Hard” sitesIt may now be possible to attempt to furtherrank sites even at this stage into whetherthey will be easy or hard to treat. This canbe done more accurately later when costsand benefits are estimated.

Easy sites are those where effective remedialmeasures can be readily identified and are oflow-cost.

Hard sites are those which do not provide aclear indication of appropriate treatment orwhere this is likely to be very costly. In theformer case the site should be selected forfurther, more detailed investigation if it hashigh numbers of accidents. In the latter caseit may be necessary to include the site in a

capital works programme for the area.

For operational purposes, the easy sitesshould be tackled first as they shouldprovide:

good return on money spent;

an immediate improvement in theaccident record (- useful argumentfor allocation of funds for futureyes);

an important psychological boost tostaff to see successful results fromimplementation of schemes




4.0: INTRODUCTIONThis chapter is concerned with collectingfurther data about the sites now selected forstudy, and using these to diagnose what arethe common prime contributory factors thathelp explain how the road users involved inthe actual collisions.

This in-depth analysis of an accident site,area or group of road users is necessary inorder to formulate an appropriate remedialmeasure. The following sections consider asingle site analysis, the principles applyingalso to mass and route action approaches.

STEP 4 Collection Of Further DataAnd Analysis

4:4.1 Collision DiagramsHaving produced a working computer filefor each site, inspection of all this accidentdata and relevant police records is essential.It should be related to a plan of the areashowing all on-site features relevant to thestudy period.

It is suggested that attention should first befocused on injury accidents (the mostreliably reported) unless these are very smallin number.If accidentpattems are not obvious from theseaccidents (discussed below),then itmay be helpful to include the damage-only accidents where available.

It is strongly advised that the POL27sketch plms and accident description areretrieved by using the accident referencenumbers for each accident.The values ofdata items which will uniquely define aparticular accident record are:

State codeDistrict codePolice Station no.Year

Accident Reference no.

Copies of the sketch plans of accidentsreferenced by the above numbers from 1992onwards can currently be obtained onapplication from:

Accident Research Unit,Fakulti Kejuruteraan,

Universiti Pertanian Malaysia,43400 Serdang,

Selangor Darul Ehsan

Having obtained these and printed outthe computerised record for each accidentusing MAAP, the next step is to producecollision diagrams at each site by drawingan approximate plan, preferably to about1:500 scale showing the main site features(eg.kerb lines,street furniture, trees andbuildings,and road markings. Details for thisshould have been noted/drawn during theinitial site visit (Step3).

On this plan, the POL27 sketch plans foreach accident should be referred to in orderto mark the positions of the accidents, andalso the approach and intended departurepaths of the vehicles immediately involved.An example of such a collision diagram fora crossroads where there were 10 injuryaccidents is shown in Fig.4.1. It issuggested that standard symbols be usedfor this as given in Appendix E

The most important use of the collisiondiagram is toprovide a starting pointfor the classification of each accidentinto clusters.

4:4.2 Classiflcation Of Accident TypesAs was stated in Chapter 1,accidentsare generally multi-factor events and itis thus important not to try to assign asingle cause to each accident during theinitial examination of data.To do this


CHAPTER IVDIAGNOSIS



could mask underlying factors which canoften be treated by simple low-cost remedialaction.In practice an accident can beassigned to many underlying factors. Forexample, depending on circumstances,the basic single collision type shown inFig.4.2 might be assigned to any of thefollowing accident factors:

Approach visibility restrictedViolation of mandatory signOvershooting give way lineCollision on restart from give waylineObscured give way signGive way line worn away orconceaIed by uneven road surfaceJunction ahead not apparent fromside roadExcessive speed of main road traffIcUneven lighting concealing mainroad vehicles

This list is not exhaustive, but illustrates thefact that a single collision type can beclassified according to many factors oraccident types. Some of these may suggest asuitable treatment whereas others may not

thus the aim should be to assign accidents toa class for which there is a remedial action.Unfortunately, many of these underlyingfactors will not appear in the accident reportor original police file.

Let us consider again Fig.4.l where theaccidents could be classified as:2 double cross-overs (crossing both mainroad streams), a right turn, a left tum off (ornose-to-tail), and a pedestrian accident. Atfirst sight no distinct accident pattern isrevealed and thus no indication of myremedial action that would help. If left hereno improvement to the junction would bemade.

However, after reading the writtendescription of the POL27 form it wasdiscovered that all 4 drivers pulling out ofone minor road (fig 4.2) stopped first butcollided with a main road vehicle on restart,because their “view to the right wasobscured by street furniture or parkedvehicle”. The rear-end collision in fig.4.1occurred when the first vehicle braked for athird vehicle emerging from the side roadbut whose vision was masked by street




furniture. Similarly the pedestrian steppedout from behind the same street furniture.Hence all 6 accidents could be assigned tothe class: “view to the right obstructed”, andthus the necessary remedial action is clear;ie. remove the obstructions.

4:4.3 Searching For A Dominant AccidentPattern

Consider the collision diagram in Fig.4.3where again on first viewing there does notappear to be any pattern which indicates atreatment. There is a need to re-classify theaccidents to produce a dominant accidenttype in which there is at least one commonfactor which could be treated. The simplestway is to produce a stick diagram and,because every accident cluster is unique,using a standard stick format may be toorestrictive. Such a stick diagram has beenproduced manually in Fig.4.4.

Note that although other sticks can beproduced and automatically sorted usingMAAP, the investigator is restricted to usingonly the computer coded items of POL27.Even if MAAP or other software packageswere used, manual checking is almost

always necessary to verify and add data tothe computer grid. In Fig.4.5 additionalinformation obtained by reading the textdescription, looking at the sketch diagrams,and observations during the site visit, hasbeen incorporated by adding additionalitems and symbols (such as the “obscuredvision” and “double cross over” taking intoaccount main road direction).

To help reveal common factors a usefultechnique is to cut up the grid to produceindividual sticks for each accident. Thesecan be rearranges repeatedly on a new sheetof paper until a pattern is noticed. Anexample of one rearrangement (by mainroad direction and collision type) is shownin Fig.4.5). Pattern recognition is a skillwhich improves with use.

In the example it can be seen that theeastbound and westbound accidents revealdifferent characteristics. The westbounddirection all possess “visibility obstructed byparked vehicles and trees” and the remedialaction may involve new or enforced parkingrestrictions and tree lopping.




On the eastbound approach, all accidentsoccurred on a wet road surface, the wetsurface condition for the whole site beingstatistically no worse than the ‘norm’. Thefurther data required in this case are skidresistances and any reasons why theeastbound approach may be wetter thanwestbound. In the subsequent site visit itwas found that skid resistance was indeedconsiderably lower on this side due toreinstatement of the west side followingextensive utility works. Also, lorries leavinga nearby plant were regularly depositingwater on the road on the eastern side.Furthermore the “Give way” line on theminor road southern approach was wornaway and partly concealed due to a surfacedepression.

4:4.4 Human Factors Need To BeConsidered

Human factors are important to theroad engineer as the roadside environmentconstantly presents visual cues to the driveras to the nature of the road ahead. Driverstend to drive on expectancy in that whenthey see a wide, straight road ahead with no

junctions they will increase speed, andthey may use a line of trees or telegraphpoles to gauge the sharpness of a bend aheadand so judge how much to slow down.

Sometimes, however, the environmentgives false visual cues. These are known as“perceptual traps” and are where somedrivers are misled by the visual appearanceof the road, commonly failing to recognisethe presence of a give way junction aheador a bend.

Unfortunately, the road engineer is unlikelyto have the opportunity to interview driversinvolved in accidents at a problem site. Butby relating the dominant factors from thepolice reports to his own site observations itis often possible to identify contributingdefects in the road system.

4:4.5 ExampleA major-minor cross-roads had recentlybeen improved on the major road armsby local widening and installation ofclearly-marked right-turn bays.However, concern was expressed over the




the number of accidents which werestill occurring.

Only one year of accident data wereavailable, and Fig.4.6 gives a MAAP stickdiagram for this period which in this caseincludes all recorded accidents. It can beseen immediately that most (>90%) of theaccidents were either right angle, side orside swipe impacts which implies collisionsbetween one vehicle approaching thejunction on the major road and anotheralong a side arm.

Most vehicles classed as “at fault” weretravelling westbound (DIR=7), though fourof the sixteen accidents involved eastboundvehicles. There does not appear to be anypattern to the time of day or day of week onwhich the accidents occurred. Also therewere only four accidents during the hours ofdarkness (the junction is lit) and only oneaccident on a wet road surface.

Fig.4.7 shows the sorted stick diagramafter viewing the POL27sketch diagrams todetermine primarily which direction themain road vehicle was travel1ing prior to the

right-angle collision. Ideally, the policeaccident descriptions should also be read (asshould witness statements, if available) todetermine whether any other factors couldbe added to the stick. It is clear that manydrivers in these accidents were failing togive way to oncoming traffic at the stopline, and as no further information could beobtained from POL27, the essential sitevisit should now be carried out.

STEP 5: Site Studies And Analysis

4:5 RELEVANT DATA FROM SITEBefore embarking on expensive new datacollection studies it is important to ensurethat all existing data about the site has beenobtained. Having studied this, together withthe accident analysis above, it should thenbe possible to decide on studies which arerelevant to the actual safety problems at thesite.

4:5.1 Simple ObservationIt is possible that obvious difficult featuresof the site may have been observed at theinitial site visit. However, with a moredetailed knowledge of the types of accident




that have occurred, and also by drivingthrough the site making the samemanoeuvres, the investigator is now likely tobe able to notice new features.

Some of the most useful questions an investigator should ask are:

a) Are accidents being caused by thephysical condition of the road or adjacentproperty, and cm the problem be eliminated or corrected?

b) Is a ‘blind’ corner or restricted sight-lineat a junction responsible? If improvementis impossible, have steps been taken towarn drivers?

c) Are the existing signs, signals andmarkings performing the job for whichthey were intended? Have conditions atthe site changed since the devices wereinstalled? Are replacements needed?Could the devices be causing accidentsrather than preventing them?

d) Is traffics properly channelled tominimise accident occurrence?

e) Would accidents be prevented by the prohibition of any single movement suchas a right turn at a minor road?

f) Could some of the traffic be diverted toother (safer) streets where problems areunlikely to be transferred?

g) Are night time accidents out of proportiontoday time ones thus needing specialnight time protection, eg reflectorisedsigns, street lighting or traffic signals?

h) Are there any particular times of day, yearor weather condition when accidents arecommon?

i) Do conditions indicate the need foradditional levels of law enforcement?

4:5.2 ExampleContinuing the previous cross-roadsexample, figs.4.8 and 4.9 show views of theapproach to the junction fromeach minorroad arm. The minor road is long andstraight and relatively wide such thatapproach speeds of some drivers areprobably quite high.




Despite the fact that there are stop signs, thevisual cues to the driver provided by thekerb lines, line markings and light columnssuggest that the road is continuous without abreak, whereas it is, in fact, crossed by amajor road. It is possible that even if adriver is a regular user of the road, the factthat he has been travelling a considerabledistance in a fairly straight line could meanthat he is not paying full attention and maythus fail to stop at the junction :there is thenobviously the chance of a collision with amajor road vehicle of the side impact typewhich can often result in injury.

To improve this cross roads the engineershould concentrate on breaking up the longdistance view, such that the illusion of acontinuous road is removed. A relativelylow-cost method of doing this would be toconstruct new offset traffic island in thecentre of each minor arm carriageway withsuitable chevron ghost islands and arrowsigns. There is also likely to be a need toshave some area off the existing splitterislands to maintain adequate road width inthe curved chicane created (see Fig.4.10).The carriageway's intersection by the majorroad should then be much more obvious toapproaching drivers.




As the junction carries relatively lowvolumes of traffic (including motorcycles),an alternative treatment could be theinstallation of aroundabout on which aremounted chevron boards opposite eachapproach arm. This would also have theadditional benefit of slowing down trafficapproaching on all arms of the junction(eg.see Fig.4.11).

4:5.3 Other Observational Measurements

It is obviously desirable to have as muchinformation about a site as possible whenmaking decisions about how best to improveits safety. It is, however, recognised thatadditional observation studies may bedifficult for some road authorities to carryout for reasons of cost and manpower.

Nevertheless, some of the followingmeasurements or techniques would beworthwhile in certain circumstances toprovide justification for decisions onremedial action.

Table 4.1gives a list of the morecommon types of accident problemswith studies that are likely to beappropriate. However, it must be notedstudies will not be essential in every case.Further details of site studies canbe obtained from ref.1

4:5.3.1 Traffic Flow

A range of traffic data can be collected toassist with analysis, and this needs to beappropriate to the task in hand andcomparable with the accident data, eg. sameyear or particular day of week.

To help decide on the most appropriateprovision for a particular manoeuvre(eg. right turners)at a junction, it isnecessary to know the numbers of driversnormally making this manoeuvre.Comparing previous counts with morerecent ones may reveal some changes intraffic pattern that could help to explainchanges in the accident pattern.

Although automatic axle counters can beused to measure straight road flows quiteaccurately, manual counts will probably berequired to obtain turning manoeuvres atjunctions. Although time-consuming toobtain, this method has the advantage ofproviding more accurate vehicleclassifications (eg. for motorcycles, buses).

If pedestrian accidents are a problemthen the engineer will need to knowhow many pedestrians are crossing theroad and where they do s.

Guidance on carrying out vehicle flowcounts is given in ref.2.




4:5.3.2 Speed MeasurementsExcessive speed is frequently reported asbeing a major contributory factor inaccidents, and there can be no disputing thefact that safety margins are reduced and thelikelihood of escaping injury in a collision isreduced with increasing speed.

However, to provide evidence for asuspected speed problem at a particular site,speed measurements need to be taken. Roadsurface vehicle detectors linked to electronictimer counters provide accurate spot speedmeasurements if installed correctly, buthand-held radar guns have perhaps proved tobe more popular a method due to their easeof use. However, care needs to be exercisedin the use of radar guns to avoid secondaryreflections from oncoming vehicles whichcan cause incorrect readings. For example,they are usually impractical for busy dualcarriageways unless used from an overheadbridge.

accidents, and there can be no disputingthe fact that safety margins are reducedand the likelihood of escaping injury ina collision is reduced with increasingspeed.

The siting of a radar meter is veryimportant. It must be as inconspicuous aspossible so as not to affect drivers, choice ofspeed and away from bus stops, parked cars,junction mouths etc. The meter should bepointed as straight as possible along the road(in line with traffic movement):an error of10 degrees either way will cause the meterto under-read by 1 1/2 %.

A sample of at least 100 (preferably 200)should be taken comprising all freely-moving vehicles (or platoon leaders) toobtain a good estimate of the true mean and85th percentile speeds. The standarddeviation of the sample should be about onesixth of the mean. If it is much higher thanthemean (say, one quarter) or much lower(say, one tenth), then the measurementsshould be regarded with suspicion.

4:5.3.3 Photography And Video.The use of still photography or video takenfrom various positions (eye height, side orplan view) can be invaluab1e forpresentations or measurements made in theoffice.

Using colour video with a tenth second timedisplay facility taken at various times of day,the movement of vehicles and pedestrianscan be studied repeatedly in the office.Studying the road user behaviour in this waycan sometimes provide valuable clues as towhy accidents are occurring and whetherthere are any deficiencies in the sitegeometry which could be improved. If thereare indications from the accident data of,say, a peak hour or wet weather effect thenfilming should be made in the sameconditions.

4:5.3.4 Traffic Conflict StudiesIt is often difficult to establish the factorsthat lead to accidents from accident dataalone due to incomplete or unreliableinformation. An additional measure whichcan assist in the diagnosis of problemsinvolves the observation of conflicts or“near-misses”. Conflicts are those eventswhere there is a possibility of an accident,but where a collision does not occur becauseone or more of the parties involved takesavoiding action.

A conflict study is simply a formalisedmethod of observing the interaction oftraffic at a location and recording the morehazardous events. There is obviouslysubjectivity involved in the identification ofconflicts, and observers do need to becarefully trained to maintain conformity ofresults. Several slightly varying techniqueshave evolved in different parts of the world3

and a relatively easy-to-learn and reliabletechnique has been developed over a numberof years by TRL3,4.

In a conflict study the numbers of conflictsare recorded and graded according to a scaleof severity. This ranges from controlled




slight braking to extreme emergency evasiveaction. The resulting data, usually expressedin the form of daily rates of particular typesof conflict, should be used in conjunctionwith accident information to identifyparticular manoeuvres, road user groups, orsite factors which contribute to a poor safetyrecord.

Conflict studies do have limitations to theiruse, and advice on the choice of sites,numbers of observers, length of studyperiods, etc .is given in ref 4.

4:5.4 Example Of A Site StudyFig.4.13 (from ref.5) shows the collisiondiagram over a period of two years for anurban T- junction between two one-wayroads in Seremban.

The stick diagram produced by MAAPis shown in fig.4.14 and this has been sortedaccording to collision type and severity ofaccident.

It can be seen that the majority of collisions(33 out of a total 68) are side swipes(including all side impacts). Six of these

involved injury and all 6 injuries weresuffered by motorcyclists. These collisionswere chiefly between vehicles turning rightout of the side road, Jalan Sheikh Ahmad,and merging with main through traffic.

It is also likely that the 12 rear-endaccidents were as a result of vehiclesbraking for these merging vehicles furtherupstream. The other main type of injuryaccident, comprising one fatal and fourinjury, that occurred at or near the junctionwere between pedestrians and motorcyclists.Pedestrians frequently do not notice thesmaller visual area that a motorcyclistpresents compared with a 44 wheeledvehicle.

There does not appear to be any noticeabletime of day or darkness effects in theaccident pattern. Owing to various tuneconstraints, only a one day study could becarried out at this junction, but it wasdecided that this should include collectingdata on traffic conflicts, approach speeds,vehicle manoeuvre now and pedestrian roadcrossing flows. The traffic flows are shownin Fig 4.15 and main conflict counts in Fig4.16.


Fig. 4.13 Collision diagram (accidentsover 2-years) for junction inSeremban



It can be seen that the merge type of conflictwith vehicles from Jln. Sheikh Ahmad wasthe most common due to relatively highmerging flows. Drivers making thismanoeuvre, particularly motorcyclist,werefrequently observed relatively high mergingflows. Drivers making this manoeuvre,particularly motorcyclist, were frequentlyobserved as possible in order to use eitherthe access road on the left (Jalan Khalsasee Fig.4.11) or adjoining petrol station.From Figs.4.15 & 4.16 it can also be seenthat the frequency of pedestrians crossingthe road is very high with a maximum of890 in one hour. Conflicts with vehicles tendto occur mostly when business activity ishigh particularly in the morning.

Approach speeds of freely-moving vehicleswere also measured using radar (seeFig.4.17) with a mean speed of 30km/h and85th percentile of 37km/h, vehicle speedswere not considered to be excessive.

The proposed accident countermeasuresat this example site will be discussed inthe next chapter.





REFERENCES

1. RADIN UMAR R S. Panduan Diagnosis dan Rawatan Kemalangan Jalan Raya. To be published by Dewan Bahasa dan Pustaka, Kuala Lumpur - 1995

2. CHE MAT BAHRI BIN HJ KASRI. Traffic Survey and Studies. Institut Kerja Raya Malaysia training reference: JLN/RA/201/1 IKRAM, Jalan Serdang, 43000 Kajang-1989.

3. ASMUSSEN, E. International Calibration Study of Traffic Conflicts Techniques. NATO ASI Series F: Computer & System Sciences. Springer-Verlag, Berlin,Heidelberg, New York, Tokyo - 1984

4. TRANSPORT & ROAD RESEARCH LABORATORY. The Traffic ConflictTechnique Guidelines. TRRL. Institution of Highways and Transportation, 3 Lygon Place, Ebury Street, SW1W 0JS, London - 1987

5. BAGULEY, CJ, & RADIN UR SOHADI. The improvement of accident data qualityin Malaysia. In: Proceedings of First Malaysian Road Conference 1994. JKR, RoadsBranch, Jalan Sultan Salahuddin, 50582 Kuala Lumpur - 1994



5.0 INTRODUCTION This chapter discusses the steps of se1ectinga package of possible countermeasures for asite and of prioritising the potentialtreatments and sites. This is done by simplydeciding on appropriate objectives of tilevarious safety strategies based on achievingsatisfactory accident reductions whichmatch or exceed the expenditure planned.

STEP 5: Select PossibleCountermeasures

5:6.1 Objectives Of CountermeasureScheme

For Malaysia, the precise objectives for thefour accident reduction strategies outlined inChapter I (Section l:4) will need to bedecided based on local experience but thoseadopted in the UK are given below as aguide. The First Year Rate of Return(FYRR) is a measure of the net benefits interms of accident reductions from thescheme expressed as a percentage of thetotal capital cost. This is defined fully laterin this chapter in Step7.

5:6.1.1 Single Site ObjectivesTo achieve an accident reduction ofat least 33%at treated sites.To obtain a significant FYRRTo carry out the remedial work at acost per site not exceeding a fixedmaximum amount

An average FYRR of 50% for schemesshould be achievable nationally. As timegoes on schemes with a smaller FYRR maybe worth considering provided that theymeet the other two objectives.

It is suggested that a maximum ofRM25,000 be an appropriate level for thefirst application of accident remedial work.Thereafter this maximum may be increased

between RM250,000 and RM500,000.

5:6.1.2 Mass Action Objectives

To achieve an accident reduction of at least 15% at treated sites for eachplan.To obtain a FYRR of not less than40%.To carry out the remedial work at acost per plan not exceeding a fixedmaximum amount.

The maximum scheme cost is likely todepend on the type of measure used andthe number of sites covered.

5:6.1.4 Area-Wide Objectives

To achieve an accident reduction ofat least l0% within the area coveredby the plan.To obtain a FYRR of 10% to 25%.To carry out the remedial work atminimum cost. The maximum sumwill depend on the area size andinclusion of environmentalenhancements.

5:6.2 TreatmentsHaving identified dominant accident types ata location or area under study, this willhopefully give an indication of anappropriate remedial measure (or package ofmeasures if there is more than one accidentgroup).

It is desirable to consider a number ofalternative proposals for each site. For everyproposal it should be checked that:

a) The measures are likely to decreasethe type of accident at which it isaimed


CHAPTER VSELECTION



b) No further increase in other types ofaccident is likely to occur as a result ofthe selected measure.

c) There are not likely to be anyunacceptable effects on traffic movementor the environment.

It should be stressed that safety at thesite under study should not be the onlyconsideration when choosing an appropriatecountermeasure. The effect of that measureon the surrounding network should beestimated. For example, a self-enforcingspeed reducing device like a series of roadhumps on a local collector road may havethe effect of making a large proportion ofdrivers choose an alternative route alongquieter residential streets. As well as beingundesirable by residents of these streets, thesafety will also most probably be worsenedby the increased traffic now.

The following tables (5.1 to 5.3) give alist of simple, chiefly low-cost, measures forgeneral, urban and rural situations whichhave been found to be effective. Whereavailable, the average percentage reductionin accidents that has been achieved1,2 is alsoincluded. It should be noted, however, thatthe list is based largely on experience in theU.K. and Australia3,4 and should thereforeonly be used as a guide or “ideas” list. It islikely that some of the measures will not beapplicable in Malaysia and the reduction inaccidents will almost certainly be different.It is thus very important that all remedialmeasures are properly monitored andevaluated, and results published or at least,centrally recorded so that a similar list basedon actual Malaysian experience cm be builtup.

If more than one group of accidents hasbeen identified at a site, then the remedialwork may consist of a package of measureswith each one designed to reduce aparticular accident group. It does not, ofcourse, follow that the total effect of such acombination of measures at one site will be

the sum of the individual percentages givenin these tables.

It is also recommended that reference5

be used as a source of ideas on many othertreatments for typical blackspots, and thatthe reader keeps up-to-date with newtechniques.

5:6.2.1 ExampleLet us consider the same example T-junctiondiscussed in detail at the end of the previouschapter (Section 4:5.4|& ref.6). It is clearthat the vehicle sideswipe and pedestriancollisions problems should be whereattention is focused in designing remedialaction. In view of the former type ofaccident tending to involve motorcyclist, itwas decided that the best policy would be torestrict the crossing manoeuvre and make allturning vehicles perform more of a mergetype manoeuvre. This could be done by firstnarrowing down the two-lane flow alongJalan Sheikh Ahmad which currently joinsthe main road, Jalan Yam Tuan (seeFig.4.15) into a single lane. This would havethe extra advantage of providing more areawhich can be utilised for motorcycleparking.

A solid delineator kerb was suggested forthis purpose as shown in the sketch inFig.5.1.This kerb is extended along JalanYam Tuan so that the merge is actuallycarried out further downstream wherevehicles are travelling parallel to oneanother, and thus main road drivers have aclearer view of merging vehicles. Thissmoother merge should also help preventqueuing along Jalan Sheikh Ahmad despiteits exit now being restricted to a single lane.

The solid channelisation, which willreduce the width of the main road slightly,will need to be extended beyond Ja1anKha1sa and the petrol station to preventdrivers making the immediate crossingmanoeuvre to the left hand side (100 to150vehicles per hour - see Fig.4.14).Thisrelatively small proportion of the traffic will




however, now need to use a road on the left(slightly further downstream) to access theseentries.

Two proposals are shown in the conceptsketches of Figs.5.l and 5.2 to deal with thepedestrian conflict problem. The first is tobuild a footbridge which would only befeasible between Jalan Sheikh Ahmad andJalan Khalsa without affecting existingbuildings.

As there are considerable numbers ofpedestrians at present crossing the roadfurther upstream (Fig.4.14), it wouldprobably also be necessary to installextensive lengths of pedestrian guard rail tochannel pedestrians to the footbridge. This isobviously an expensive solution.

The second option of installing a pedestrianrefuge, as shown in Fig.5.2, is muchcheaper. The refuge should make it easier

for pedestrians as they only have to makegap judgments about one stream of traffic ata time. Also, this refuge, together with thenew chicane now already at this point,should also help to slow down traffic in thisvicinity. Large road studs along theboundary line of the hatched area anddirection arrows on the refuge wouldalso be required to help minimise thelikelihood of co11isions with the newrefuge.

As well as being much cheaper thissecond option is preferred as it is like1ythat many pedestrians would not chooseto climb the footbridge.

5:6.3 Approaches To Area-WideTreatment

Where accidents are widely dispersed, oftenin urban areas, over several squarekilometres rather than at obvious individualsites, an area-wide treatment may need to beconsidered




A road hierarchy should be drawn up by aroad authority where residential streets,access roads, local distributors, districtdistributors and primary distributors aremarked together with land-use (see Fig.5.3).

This can then be used as a base map onwhich to mark road accidents, vehicleand pedestrian flows.

There is a wide variety of treatmentsthat can be used in residential areas but goodconsu1tation with local residents is alwaysstrongly recommended.

Traffic calming can generally be regarded asways in which vehicle speeds can bereduced from an average of 50km/h down to30km/h.

The safety objective is to reduce both thenumber and severity of accidents, especiallyto vulnerable road users. This is usuallydone with self-enforcing speed reducingmeasures like chicanes, traffic throttles, roadhumps or speed tables (see Figs.5.4 to 5.9)

The main principle of traffic calmingtechniques is that they still permit motorisedtraffic to use the same route which they areunable to do with more restrictive measureslike road closures, turning bans and one-waytraffic. Although limited use can be made ofthese latter measures (eg.Fig.5.5), they arerarely popular with residents and can lead toaccidents being transferred to other areaswhich become used as “rat-runs”.




It should be remembered that solutionsto a detailed study at a site may notexclusively involve civil engineering works.An integrated approach to improving roadsafety should really be adopted wherebyroad safety education and training may needto be combined with an engineeringmeasure. For example, the introduction of anew signa1 controlled pedestrian crossing ina village may require a local publicitycampaign to inform pedestrians and drivershow to use it together with training forchildren in the local school(s).

STEP 7: Priortise Treatments & Sites

5:7.1 Estimating Accident SavingsThe standard approach for the ranking oftreatments is to carry out a cost-benefitanalysis based on estimated benefits of thescheme and simply place these in priorityorder on the basis of the best returns.

However, if there is currently little or nodata on which to make an estimate of thelikely effectiveness of a treatment, thenperhaps the best way to proceed is toimplement the lowest cost schemes first asthese are likely to provide the greatestoverall benefit. If the least cost schemeproves in practice to be ineffective then thea1ternative schemes in order of increasingcost should be tried. In most uses apessimistic estimate can be assumed to be anaverage reduction in accidents of around25-33%of a1l accidents.

In these applications it is recommendedthat temporary materials be employedwhere possible for initial trials; for example,pre-cast concrete slabs tied together andpinned to the road surface to try a particularsize and position of splitter island (seeFigs.5.10 & 5.11).

An economic assessment of projectedschemes is important to ensure that thebenefits likely will be greater than the costof implementing and maintaining thescheme and that the best value for money isobtained.




There are two methods of economicassessment used for this purpose:

i) First Year Rate of Return(FYRR),and

ii) Net Present Value(NPV)

Both methods need the following basicinformation:

a) The capital cost of the scheme.b) An estimate of al1 benefits

(monetary value)expected to result.c) An estimate of all disbenefits.

5:7.2 First Year Rate of Return (FYRR)This is simply the net monetary value of theaccident (and any other) savings anddrawbacks expected in the first year of thescheme, expressed as a percentage of tiletotal capital cost.

FYRR (%) = Benefits (1st year) x 100Capital costs

where benefits = accidents savings +

change in maintenance costs(+/-)+

change in journey costs(+/-)

Unfortunately, at present the only availableaccident costing used in Malaysia is thatproduced in 1985 (see Table 5.4 - fromESCAP7).

However, applying national inflation figuressince that time, figures for 1995 areestimated in Table 5.4; and using the recentnumbers of each severity class of accidentsin Malaysia, the average cost of an injuryaccident in 1995 is approximatelyRM33,000. It is likely that this figure isnevertheless an underestimate, and it ishoped that a study will be conducted soon todetermine more up to-date and realisticvalues for Malaysia. A column for the mostrecent national accident costings has thusbeen left in Table 5.4.

Thus let us consider, as an example, ajunction which had l2 injury accidents in3 years, and nine of these involve sidecollisions with drivers overshooting the Stopline - these being the treatable group ofaccidents. If the target FYRR is 50%, thenthe maximum budget for the scheme may becalculated as:

%FYRR = Annual Acc. Saving x 100Scheme cost

50 = (9 x RM33,000 /3) x 100Scheme cost




Scheme cost = RM99,000 x 10050

= RM198,000

That is, the scheme should not cost morethan RM198,000 in order to achieve a 50%rate of return.

A more detailed assessment may, however,be needed with schemes where trafficaccidents and traffic levels are expected tochange considerably from year to year. Forexample, a scheme with an 80% FYRR maynot be worthwhile if subsequent roadclosures due to construction of a plannednew road, say, restricts the benefits just oneyear.

5:7.3 Net Present Value (NPV)This type of evaluation expresses (in asingle lump slim) the difference betweencosts and benefits of a scheme which mayoccur over a period of several years.

Unfortunately, it would be incorrect tosimply assume that year 1 benefit can besummed to obtain the overall benefit overthe life of the scheme. This is becausesociety, in general, prefers benefits whichoccur sooner rather than later. Futurebenefits must therefore be adjusted , or“discounted” before being summed to obtaina “present value”.

The current rate used by the Treasury forhighway schemes is l1% which means thatfor each RM l of benefit occurring this year,

if this also accrues next year then this isvalued at 11% 1ess, ie.89 Sen. A furtheryear's delay will reduce the benefit again by11% of 89 Sen, ie.79 Sen, and soon. Thesefigures can be summed over the life of thescheme to obtain the Present Value ofBenefits (PVB).

The overall economic worth of the schemeis then obtained by deducting the PresentValue of Costs (PVC){these may also have to be discountedif they are spread over more than oneyear}:-

NPV = PVB-PVC

The scheme is only usually consideredworthwhile if this figure is positive.

5:7.3.1 Example of NPV assessment.

Let us assume that the expected costs of ajunction redesign will be initiallyRMl00,000 spread over 2 years with annualmaintenance costs over the next 5 years (thelife of the scheme) of RM8,000.

The benefits are always difficult to estimateand will often require a simple educatedguess. If in this case we assume that 4 injuryaccidents over the first two years(2 per year)will be saved, and this will reduce to 0.5 peryear following that due to changes in traffic.This equates at present to RM66,000 for twoyears followed by RMl6,500 for the remain-ing 3 years. The Net Present Value iscalculated in Table 5.5 to be RM6,865.




In cases where the estimated benefits do notvary throughout the scheme, the calculationof NPV is simplified by the use ofcumulated discount values and these aregiven for various discount percentages inAppendix F.

For example, for a benefit of RM20,000 perannum over 5 years with reference toAppendix F, the net benefit at 11% discountrate would be:

RM20,000 x 3.57 = RM71,400

5:7.4 Priorities For ImplementationThe economic criteria for schemeassessment using the NPV approach are:

all schemes where NPV is positiveare worthwhile in economic terms;

for a particular site, the mostworthwhile option is that with thehighest NPV;

all options are ranked in order oftheir NPV/PVC ratio [the highestratio at the top of the list].

If funds are limited, those with the highestNPV/PVC ratios are preferable on economicgrounds.

Table 5.6 shows an example of a remedialworks priority programme ranked in termsof the schemes, NPV/PVC ratio for a 5 yearperiod.

It can be seen that in this example theNPV/PVC ratio gives only a slightlydifferent ranking of the sites to that usingFYRR. Using this listing, a line can bedrawn for a particu1ar budget: in this useRM350,000. The full 1ist of l0 sites couldonly be implemented if a budget ofRM500,000 were allocated.

If the authority is receiving local political orother pressures to treat a site which is




outside this list or below the cut-off level,then the table can be used to point out thatresources should be concentrated at the siteswhere greater benefits are likely to occur.This is more 1ikely to yield the bestcontribution to the nation’s casualtyreduction targets.

In some uses a site may be at a locationwhich is included within a major capitalworks programme such as a flyover ortraffic signals. If the time at which these arescheduled for introduction is fairly close, itmay be best to “do nothing” at this stage andincorporate necessary work within the majorscheme. If, however, the scheme is unlikelyto be carried out for 2 or 3 years, thenshort-term (perhaps lower-cost) measureswill probab1y be justified .

For this reason and others which mightlead to “s1ippage” in timetables, it is alwaysworth investigating more sites and preparingmore schemes than can be carried out in the

current budget period to allow for theseminor re-allocations of funds.

In practice “easy” sites are normally besttackled first to yield cost effective results asquickly as possible.

However, it is likely that the “harder” sites,which may require more staff resources tostudy extensively, will have high numbers ofaccidents. These sites should not thus be puton one side and forgotten about.





REFERENCES

1. ROYAL SOCIETY FOR THE PREVENTION OF ACCIDENTS. Road safetyengineering manual. RoSPA, Cannon House, The Priory Queensway, B4 6BS,Birmingham - 1992.

2. ACCIDENT REDUCTION 2000 GROUP. Progress Report December 1993. Transportation Dept, Hertfordshire County Council, Goldings, SG14 2PY,Hertford - 1994.

3. NATIONAL ASSOCIATION OF AUSTRALIAN STATE ROAD AUTHORITIES. Guide to traffic engineering practise: part 4-Road crashes. NAASRA, 2, Dind Street,PO Box 489, Milsons Point, NSW 2061-1988

4. ANDREASSEN, D C. Strategies for safety problems. Australian Road ResearchBoard. Research Report ARR163. ARRB, 500 Burwood Highway, Vermont South,Victoria-1989

5. TRANSPORT & ROAD RESEARCH LABORATORY. Towards safer roads in developing countries: a guide for planners and engineers. TRRL & Oversea’sDevelopment Admin., Old Wokingham Road, RG11 6AU, Crowthorne-1991

6. RADIN UMAR RADIN SOHADI. Analisis Terperinci Kemalangan Jalan Raya:Projek Pilot Seremban, Shah Alam dan Petaling Jaya. JK3P, Laporan Penyelidikan No. 4. Majlis Keselamatan Jalan Raya Malaysia, Wisma Semantan, JalanGelanggang, 50490 Kuala Lumpur-1993

7. ECONOMIC AND SOCIAL COMMISSION FOR ASIA AND THE PACIFIC.Report on improvement of the traffic accident recording and analysis system in Malaysia. UN ST/ESCAP/478, Bangkok-1985



6:0 INTRODUCTIONHaving selected an appropriate measure orpackage of measures to deal with theaccident problems at a site or area, the nextstage is detailed design and construction. Itis not within the scope of this Guide tocover in depth the actual detailed design orphysical implementation. This will generallybe the responsibility of another appropriatedepartment. However, it is essential that theteam who made the scheme recommendationcontinue to be involved.

The road safety audit is discussed andgeneral advice on the safety of constructionwork noted.

STEP 8: Detailed Design AndInstallation

6:8.1 Detailed DesignAs stated above, the next stage afterselecting an appropriate remedial measurewill usual1y be detailed design. This islikely to be carried out by a different unit tothose investigating the problems, and isbeyond the scope of this Guide. However,the design drawings will, of course, need tobe based on the proposals/outline plans ofthe accident investigators and this sameteam should also remain actively involvedwith the designers.

6:8.1.1 Road Safety AuditRoad safety audit is a means of accidentprevention rather than accident reduction(a change in philosophy to the previouschapters). It is the application of safetyexperience to ensure that future safetyproblems are not designed into newschemes. It is discussed here because ideallyan audit should also be carried out on safetyremedial work, both at the design stage andagain immediately after the schemeimplementation: that is, prior to opening tonormal traffic. Safety audit is simply the

the technical term for the systematicchecking of safety aspects of new schemescarried out on the public road.

Although it is assumed that nationalstandards will be followed in any designunless unusual local conditions dictate adeparture (which needs special approval), acombination of elements perhaps close totheir respective recommended minimumstandard, may combine to create safetyproblems. Safety audit seeks to address suchproblems .

At present the UK Institute of HighwayEngineers’ Guidelines1 are beingapplied in Malaysia but these should beamended to suit local conditions asexperience is gained.

6:8.1.2 Aims Of The Safety Audit

To ensure that all road schemesoperate as safely as possible.

To ensure that preventable potentialaccident-generating elements are notpresent in a completed scheme, forexample ,moving lamp columns tothe back of the footway.

To ensure suitable accident-reducingelements are included in the scheme, for example, "anti-skid" surfacingon down hill approach to trafficsignals, guard rail and chevronboards on unavoidably sharp bend,crash cushion before essential solidstructure.

6:8.1.3 Organisation Of The AuditSafety audit should be part of the overallsafety management strategy for the roadauthority within its Road Safety Plan. Anarbitration procedure should be agreed inuse of differences in opinion.


CHAPTER VIIMPLEMENTATION



In a road authority it is likely that safetyaudit will be carried out within the accidentinvestigation/road safety unit, thoughpreferably by more than one person. Beforedeciding on who should carry out the auditthe following should be considered:

The audit team should be independent of the design team. Itshould contain (and must certainly be led by) persons with safetyengineering experience. Aknowledge of design standards is important.

Other specialists such as trafficsignals and structural engineers mayalso need to be consulted dependingon the scheme. The police may alsobe required, particularly in the latter stages of the audit, where special road users, requirements may needconsideration.

6:8.1.4 When To Carry Out The AuditSafety audits can be performed at thefollowing stages:

Feasibility study

Completion of preliminary design

Completion of detailed design

Prior to opening to traffic

Other times on an informal basis

6:8.1.5 The Audit TaskInformation such as plans, list of standardsfollowed, departures made traffic andpedestrian counts, and accident recordsshould be collected from the design team. Itmay be helpful to discuss the purposebehind the design of the scheme and it isessentia1to carry out a site visit at a1l stagesof the audit.

Appropriate check lists1 should be usedto systematically ensure no safety problem

is overlooked. However, the audit teamshould not rely solely on these lists.

The auditors should imagine “walking” or“riding” the scheme, and should physicallydo this at the final audit stage to check, forexample, that signs are of the correct typeand in the right place, road markings andisland are correctly placed and that there areno unforseen conflicts between the treatmentand other existing site features.

Although the audit team should discusstheir findings with the design team, a formalreport should always be produced. Thisshould state the potential safety problems asprecisely as possible and should include arecommendation or options forimprovement. The recommendation shouldbe in outline form only and it may bedesirable to annotate copies of the originalscheme drawings.

The scheme should be monitored andfeedback given to the design team.

6:8.2 InstallationAs stated above, it is beyond the scopeof this Guide to include guidance on allengineering aspects of altering existingroad geometry or installing countermeasuredevices. This section is thus limited togeneral advice on maintaining safety duringinstallation.

6:8.2.1 Safety At RoadworksAccidents tend to occur at a higher rate atroadworks sites and involve more vehiclesthan on normally operating sections of theroad network. A study of major roadworksites in the UK2 found that, despite the factthat the contraflow sites were genera1ly wellsigned and laid out, accidents still occurred1.6 times more frequently than on non-road-works sections, and the percentage ofaccidents involving 4 or more vehicles was29% compared with only 8% without works.It issuspected that the ratio may beconsiderably higher than this in Malaysia,particularly at sites where advance warningsigns are poor.




It is very important, therefore, thatcountermeasure installations themselvesare made as safe as possible. The roadengineer must attempt to regularly enforcecontractors to follow the standards laiddown in Arahan Teknik 2C/853 for trafficcontrol, temporary signs and work zones at

their roadworks sites. Often with relativelyshort-term work due to the extra troublerequired, warning signs are not set outsufficiently in advance of the works site orare two few in number: this is particularlyhazardous where drivers vision of the sitemay be obscured by a bend or other traffic.

The use of modern electrically-poweredflashing arrow lights mounted on trailerstend to provide a more effective means ofattracting drivers, attention.

Attention should be paid to the use ofadequate lengths of “safety zone” or“buffer space” (see Fig.6.4) which providesan escape area if drivers fail to notice theadvance warning signs. Lengths of thesezones are specified in ref.3.

Also, tapers of traffic cones to close offa lane before the work area, or to movetraffic into other contraflow lanes, areoften not made long enough. Thestandards should again be followed toensure that the traffic movement is gradual,and thus smoother and safer.

6:8.3 Implementation logIt is important to keep a record of theprecise dates of the beginning andcompletion of major parts of the remedialwork for all jobs. This is essential for themonitoring of the scheme (see followingchapter).

Similarly, details of all costs involved,including variation orders, must be kept. Theactual costs often differ considerably fromoriginal estimates, and this record willfacilitate a more reliable cost-benefit-analysis.





REFERENCES

1. INSTITUTION OF HIGHWAYS AND TRANSPORTATION. Guidelines for thesafety audit of highways. IHT, 3 Lygon Place, Ebury Street, SWIW OJS, London - 1990.

2. MARLOW M, and R D COOMBE. A study of the safety of major motorway roadworks in 1987. Research report RR223. Transport and Road ResearchLaboratory, Old Wokingham Road, RG11 6AU, Crowthorne - 1989

3. JABATAN KERJA RAYA. Manual on traffic control devices, temporary signs andwork zones control . Arahan Teknik (Jalan) 2C/85. Cawangan Jalan, Ibu Pejabat JKR, Jalan Sultan Salahuddin, 50582 Kuala Lumpur - 1985.



7:0 INTRODUCTIONHaving introduced a countermeasure orpackage of measures it is important toestablish the effectiveness of the safetyengineering work carried out; first to checkthat nothing has gone wrong and that it isworking as intended, and later to learnlessons which may influence futuredecisions on improvements.

This chapter emphasises the need to monitorby observing the changes at the site inoperation. To evaluate these it concentrateson accident changes and describes thesimple statistical tests needed to obtain.

STEP 9 Monitoring

7:9.1 Initial ObservationsThe treated site should be observedimmediately after completion of theconstruction and regular visits made in thefollowing days, weeks or months until theteam is satisfied that the scheme is operatingin the way expected.

It is strongly advised that my earlierbehavioural measurements that were madeduring the investigation stage of Step5 (eg,traffic conflict counts, speed measurements,skid resistance) are now repeated as this willlend weight to any argument for makingfurther changes at the site or, indeed,proving success. It can happen, for instance,that some feature of a scheme may producean unforseen reaction in drivers whichcreates a potentially hazardous situation.Monitoring should highlight this problem atan early stage so that appropriate action canbe taken quickly to remove this danger.

At best it may be possible to alleviate thisdanger easily, for example, by a realignmentof kerb lines to prevent a hazardousmanoeuvre. At worst, it could lead to thecomplete withdrawal of a scheme and needto reassess alternative schemes.

It is essential to carry out the monitoringeffectively, not least to avoid the “badpublicity” which could occur if a road safetyscheme was seen to be actually causingaccidents.

Recording the results of the monitoringmeasures is also important to build upa database of types of treatment and theeffects they produced to provide informationfor future safety engineering work.

7:9.2 Measures Used In MonitoringFor monitoring or measuring the effect of asafety improvement, the technique employedis usually by “before” and “after” analysis.The most important measure of success is,of course, whether the safety work hasimproved the accident situation at the site.This will always need to be assessed for ascheme and statistical methods forevaluation will be discussed in the nextStep. A simple visual method that has beenused, though is perhaps more suitable formass action plans rather than single sites, isthat cumulative accident numbers (& types)are plotted together with their cumulativemean.

Fig.7.1(from ref.1)is an example of thismethod of data presentation, and illustratesthat the daytime running headlight campaignin Malaysia was apparently being effectivein reducing those accidents related to day-time conspicuity (MSTOX = motorcyclesmoving straight or turning when otherroad users cross their path), whilst having noeffect on night-time accidents. In the tableof Fig.7.l the cumulative mean number ofrelated accidents has been calculated. Thecumulative mean is obtained by simplyadding on the average monthly accidentfrequency over the before period (in thiscase 6 months) to each month after the firstone. As long as the standard deviation is notlarge, the two comparable lines of


CHAPTER VIIEVALUATION



cumulative accidents and cumulative meanaccidents lie close together during thebefore period, but after implementationof the scheme the cumulative mean linerepresents what would normally be expectedif no action had been taken, and the amountthey drift apart (marked * in Fig.7.1)represents the effect of the measure.

However, to be sure that the random natureof accidents has been taken into account, itwill normally be necessary to wait forseveral years for a valid result to beavailable. More immediate feedback is oftennecessary which is why the above method issuggested. Other behavioural data, asmentioned in 7:9.1, can also be collected togive indications that a scheme is working.

It would, of course, be impractical to carryout detailed behavioural studies for all minoralterations, but studies may be particularlyimportant for expensive schemes like area-

wide or mass action treatments. It must benoted, however, that non-accident variableshave the disadvantage that they do not givedirect measures of the size of safetyimprovement. There are practically novariables for which the precise relation toaccidents is known. This means that ameasured reduction in mean speed, forexample, cannot be translated into anestimate for the number of accidents saved:this is a considerable drawback.

However, before carrying out a behavioural“after” study it is generally better to wait fora period of about 2 months after the schemehas been operating. This serves as a “settlingin” period during which regular users getused to a new road feature and any learningeffects have disappeared.

Some of the factors that may need to beexamined (see also Step5,Chap IV) arenoted below:




7:9.2.1 Speed Of TrafficIf speed reduction is one of the objectives ofthe scheme then speeds should obviously bemonitored. Similar and appropriate locationsshould be carefully chosen for the beforeand after studies preferably using automaticequipment. If radar guns are used then theseneed to be unobtrusive otherwise warningsignals invariably given by drivers in theopposing direction will yield unreliableresults.

The t-distribution can be used to comparewhether my changes in the mean speeds inthe two periods of measurement arestatistically significant (see Appendix G).

7:9.2.2 Traffic ConflictsAs mentioned earlier these are generally ofuse at junctions only. The “after” studyshould be carried out in the same conditionsand for the same periods as the “before”study, and preferably using the sameobservers (to minimise subjectivity betweenindividuals).

The frequencies of occurrence of conflictscm be analysed in the same way as themethods used for accidents, as outlined inthe next Step.

7:9.2.3 Traffic VolumesIf the measure is expected to affectmanoeuvres at a junction or drivers choiceof route in any other way, then it is desirableto collect traffic flow data throughout thelocal network. It may also be necessary toexpand this survey to provide origin anddestination information so that estimates inthrough-traffic can be obtained to determinehow this has been affected by the scheme.

7:9.2.4 Travel TimesIn some cases monitoring may require anestimate of changes in travel time forresidents and through-traffic. This will beimportant where traffic severance forms partof the scheme, and traffic is being re-routed.

7:9.2.5 Public PerceptionOften one of the main reasons why anarea-wide scheme has been implemented isdue to campaigns by residents for somethingto be done. One of the most important partsof an area-wide scheme, therefore, is publicconsultation .Thus, an important monitoringmeasure is how the residents and other roadusers feel about the safety elements of thescheme after implementation.

7:9.2.6 Effects On Other AreasIt is important to examine whether thescheme has led to an increase in accidents,traffic speeds and volumes in adjacent areas.

7:9.3 Control DataIn most of the above monitoring measures(and particularly accident changes) it isnecessary to take into account other factorsnot affected by the treatment which mightalso influence that measure. Examples are:a change in speed limit on roads whichinclude the site; national road safetycampaigns; traffic management schemeswhich might affect volume of traffic.

These changes may be compensated forby comparing the same “before” and“after” periods with accidents (or othermeasurements) at “control” sites which areuntreated. Control data can be either bymatched pairs or area controls.

A matched pair control site should besimilar to the treated site in generalcharacteristics and also geographically fairlyclose to it (but not close enough to beaffected by my traffic diversion). This is sothat the control will be subject to the samelocal variations which might affect safety(eg. weather, traffic flows, enforcementcampaigns).

Although the matched pair is the beststatistical method to use, in practice it isvery difficult to find other sites with thesame problems which are left untreatedpurely to carry out statistical tests. Areacontrols which comprise anumber of sitesare, therefore, much more frequently used.




when choosing control sites:

they should be as similar as possibleto treats sites;

they should not be affected by thetreatment;

there should be more than 10 timesthe number of accidents at thecontorl sites.

For example, if the traffic signals at a siteare modified then a control group of sitesmight be a11other signalised sizes in thetown. But if there were only two othersignalized junctions and these had lowerflows and much fewer accidents as did otheruncontrolled junctions, then it would bebetter to use all signalized junctions in theState.

STEP 10 Evaluation

7:10.1 The Effect On AccidentsThis step of the procedure focuses onevaluation of whether the treatment has beensuccessful in achieving its objective ofreducing the number of accidents. Thistherefore requires comparison of the numberof accidents in the target group before thetreatment with the number after treatment(with the assumption of a similar beforepattern if nothing were done), and to studywhether my other accident type hasincreased.

This Guide does not attempt to delve deeplyinto the different statistical techniques, butto suggest practical and simple ways inwhich schemes can be evaluated. Thefollowing sections generally refer to “a site”but the same techniques can be used formass, route and area-wide action as long asappropriate control groups are chosen.

The main problem when using accident datafor evaluation (even assuming highrecording accuracy) is to distinguishbetween a change due to the treatment and

that due to other sources. Some of the otherfactors that need to be considered arediscussed below:-

7:10.1.1 Changes In The EnvironmentThis feature was mentioned in the lastsection of Step 9 whereby a change in theenvironment or driving habits can affect theaccidents occurring at the study site. Forexample, a change in the nationa1 speedlimit for the class of road at the site, orclosure of a nearby junction to the siteproducing a marked change in trafficpatterns.

This feature can be taken into account by theuse of control site data but for this to bevalid it is important that these other sitesexperience exactly the same changes as thesite under evaluation.

7:10.1.2 Random FluctuationAs explained in Chapter I, the rare andrandom nature of road accidents can lead toquite large fluctuations in frequenciesoccurring at a site from year to year, eventhough there has been no change in theunderlying accident rate. This extravariability makes the effect of the treatmentmore difficult to detect; but a test ofstatistical significance can be used todetermine whether the observed change inaccident frequency is likely to have occurredby chance or not.

7:10.1.3 Regression To The MeanThis effect complicates evaluations athigh accident or blackspot sites in thataccidents at these sites tend to reduce evenwhen no treatment is applied. Even if a3.year total is considered at the worstaccident sites in m area, it is likely that theaccident frequencies were at the high end ofthe naturally occurring random fluctuations,and subsequent years will yield lowernumbers. This is known as regression to themean.




As an example consider Table 7.1 whichgives the actual numbers of recordedaccidents involving personal injury for 122nodes in the town of Seremban over a twoyear period. For sites with 5 or moreaccidents in year l there were overall feweraccidents in the following year. Conversely,sites with 4 or less acc1dents have moreaccidents in year 2. If an accidentcountermeasure had been installed at theworst 9 sites at the end of year l then ahighly significant reduction of 37% might beclaimed after year 2, even though themeasure had been completely ineffective(this same result would be obtained by doingnothing). An even higher false resu1t wouldbe obtained if the other 113 sites were usedas a control group.

Possibly the most straightforward way ofallowing for both the regression to meaneffect and changes in the environment wouldbe to use control sites chosen in exactly thesame way as the treated sites, and identifiedas having similar problems, but leftuntreated. In practice, it is both difficult tofind matched control sites and, ifinvestigated, to justify not treating them.

There has been much debate amongstatisticians over many years on this subjectand the best way to deal with it(see refs. 2,3,4,5).

The effect does, however, tend to bediminished if longer periods of time areselected. For example, Abbess et a1.3, in astudy in two counties of the UK calculatedthat regression-to-mean had the followingeffects at high accident sites(ie. more than 8injury accidents per year), on average, ontheir accident rate:-

Due to the uncertainty and complexityof allowing for this effect reliably at any siteit is suggested, therefore, that where thehighest accident sites are chosen fortreatment, then the above order of allowanceshould be made when calculating anyestimate of the actual reduction in accidentsthe countermeasures have produced.

7:10.1.4 Accident MigrationThere is still some controversy over whetheror not this effect exists but it has beenreported by several researchers 6,7,8. It issimply that an increase in accidents tends tobe observed at sites adjoining a successfully


Period of accidentdata considered

Regression to meanchange in annual

accident rate1 year 15 to 26%

2 year 7 to 15%

3 year 5 to 11%



treated site giving an apparent transfer or“migration” of accidents.

It can be detected by comparing the accidentfrequencies in the surrounding area beforeand after implementation of treatments atsites in the area with a suitable control. It isunclear precisely why this effect occurs butis suspected that drivers are “compensating”for the improved safety at treated sites bybeing less cautious elsewhere.

Again, there are no established techniquesyet available to estimate this effect for aparticular site. The first reported occurrenceof this feature 6 found an overa1l increase insurrounding areas of about 9% and a laterstudy8 of a larger number of sites estimated0.2 accidents/site/year.

7:10.1.5 Risk CompensationThis is an even more controversial effect,though related to the previous section. Thephilosophy of “risk compensation” or “riskhomeostasis theory” suggests that road userswill change their risk-taking behaviour tocompensate for any improvements in roadsafety. That is, road users tend to maintain afixed level of accepted risk, so will takemore risks when given greater accidentprotection, for example, if provided withseat belts or anti-lock brakes.

Whilst again the extent of this effect isextremely difficult to monitor, the engineershould be aware of the possibility of riskcompensation when introducingcountermeasures. For example, a schemegiving pedestrians more apparent priorityusing speed tables or raised pedestriancrossings (which give the impression ofextensions to the footway) may lead thepedestrian into taking much less care incrossing the road.

For further reading on this subject seereferences 9,10.

7:10.2 Before And After PeriodsThere are a number of points to taken intoaccount when choosing periods to comparebefore and after the treatment was applied:-

Before and after periods at thetreated site should be identical tothat at the control site.

The period during which work wascarried out should be omitted fromthe study. If this period was notrecorded precisely, a longer periodcontaining it should be omitted.

The before period should be longenough to provide a good statisticalestimate of the true accident rate (soas to remove as far as possiblerandom fluctuations).It should not,however, include periods where thesite had different characteristics.Three years is widely regarded as areasonable period to use.

The same applies to the after periodwhich ideally should also be threeyears. However, results are oftenrequired much sooner than this. Aone year after period can initially beused if there is no reason why thisshould bias the result (as long as thesame period is used at the controlsites). However, sensitivity is lostand the estimate of the counter-measure’s success should be updatedlater when more data becomesavailable.

7:10.3 Standard Tests On AccidentChanges

In evaluating a treatment the answers tothe following questions will usually berequired:

Has the treatment been effective?

If so, how effective has it been?

It is assumed that the user of this Guide will




need to interpret accident data practicallywithout necessarily understanding theunderlying statistical theory. For thispurpose it is sufficient to assume that thebefore and after accidents are drawn from anormal or Gaussian distribution.

This means that we can use the Chi-squaretest to answer the first question above, ie.whether the changes at the site werestatistically significant. However, let us firstconsider the size of that change by using thek test.

7:10.3.1 The k TestIt is possible that although accident levelsreduced at a treated site in an “after” period,the general level of accidents is alsoreducing; the “real” reduction at the site dueto the treatment thus being less than theactual numbers observed (ie. over estimatingeffectiveness). Conversely, if the generallevel of accidents is increasing anunderestimate of the treatment would beobtained. The k test can be used to showhow the accident numbers at a site changerelative to control data. For a given site orgroup of similarly treated sites, let:-

a = before accidents at siteb = after accidents at sitec = before accidents at controld = after accidents at control

then k = b/ad/c

or, if any of the frequencies are zero then1/2 should be added to each, ie:

If k < l then there has been a decrease inaccidents relative so the control;

if k = l then there has been no change relative to the control; and

if k > 1 then there has been an increaserelative to the control.

The percentage change at the site is given by

Example:Let us assume that Table 7.2 gives theannual injury accident totals for a priorityT-junction in a semi-urban area which hadStop signs on the minor road originally, butwhere a roundabout was installed three yearsago. The control data used are accidents onall other priority junctions in the Districtover exactly the same 6 year period.

Therefore, as k < 1there has been adecrease in accidents relative to thecontrols of:




7:10.3.2 The Chi-Squared TestIt is important to answer whether the abovechange in accidents was indeed produced bythe treatment or whether this occurred bychance. This test thus determines whetherthe changes are statistically significant.with reference to the above table chi-squaredis calculated by the formula:

Example:Now looking at the chi-squared distributiontable (Appendix D) and the first line (onedegree of freedom, v=1), the value for chi-square of 5.38 lies between 3.84 and 5.41.This corresponds to a value of significancelevel (on the column header line) between0.05 and 0.02, which is normally quoted asgreater than the lower level, ie. better thanthe 5% level of significance.

This means that them is only a 5%like1ihood (or l in 20 chance) that thechange in accidents is due so randomfluctuation. Another way of stating this isthat there is a 95% (100% - 5%) confidencethat a real change in accidents has occurredat the junction.

The 5% level or better is widely accepted asthe level in which the remedial action hascertainly worked, though the 10% level canbe regarded as an indication of an effect.

7:10.3.3 Group Of Sites With SameTreatment

For a number of sites, N, which have hadthe same treatment, the overall effect is arather more complex calculation, ie. bysolving the following equation for KK over allthe sites, ie. i = l to N. The other symbolsare as in previous equations.

For testing, the natural logarithm of avariable such as KK is usually found to have amore symmetrical distribution (amenable tostandard statistical treatments), and thestandard error, σ, of loge KK can beapproximated to the following:

The following ratio should then becalculated using loge of the value of KKcalculated above and its standard error fromthe previous equation:

and if this value is outside the range ±1.96(Student's t), then the change is statisticallysignificant at least the 5 per cent level.

Now to test whether the changes at thetreated sites are in fact producing thesame effect on accident rates, calculatethe following chi-squared value.




If this is significant with N-l degrees offreedom [refer to the (N-1)th] row in thetable of Appendix D, where N is thenumber of treated sites], then unfortunately,the changes at the sizes are not producingthe same effect. If non-significant, then it islikely that they are producing the sameeffect.

7:10.4 Economic EvaluationFor every scheme the evaluation shouldinclude an indication of the benefits actuallyachieved in relation to cost.

In the previous sections we have alreadyseen how we can determine a best estimateof the size of the effect on accidents.Considering again the example in Fig.7.2,the estimate of the reduction was 72.2%. Ifthe site was one of the worst blackspots inthe District, then we ought to make someallowance for the regression-to-mean effect.From Section 7:10.1.3,let us assume thisamounts to as much as 11%, such that ourbest estimate of the true reduction inaccidents due to installation of the round-about is 61.2% (72.2%-11%).

Since the original number of accidentsat the site was 20, this represents a saving of12.24 accidents over the study period. As the“before” period in this case was 3 years, thebest estimate of savings is 4.08 accidents peryear.

It should be noted that only injury accidentshave been considered here but if there hadbeen reliable numbers of damage-onlyaccidents which were also reduced, then aseparate costing of these should perhaps alsobe carried out.

Using the average injury accident costof RM 33,000 used in Step7 (see Section5:7.2), this accident saving amounts toRM134,640 per year.

This figure is then compared to the costs ofthe treatment which totalled say,RM150,000. Assuming delay to traffic due

to the treatment is negligible, the First YearRate of Return (FYRR) is simply given by:

The above FYRR figure should be roundedso 90% to give m indication of the possibleeffect of using this treatment in the future.

This is the same technique as outlined inChapter 5 and the Net Present Value figurescan also be calculated for completedschemes following the example given in thatChapter. This would be particularlyadvisab1e if there are considerable newmaintenance costs associated with theinstalled measure.

It is only by evaluating and recording resultsin this way that a listing of implementedremedial measures and their effectivenesscan be built up for the use of roadauthorities throughout the country.

7:10.5 Evaluating Overall EffectivenessThis chapter has concentrated on evaluatingthe effects of specific schemes. In additionthere is a need for the regular strategydocument mentioned in Chapter I to providea summary of the overall achievements ofroad safety programmes.

As background information in the strategydocument it is normal to present andexamine aggregate accident statistics overthe State, District or Municipality, brokendown in various ways by, for example, Classof road user, class of road. These aggregatefigures can be useful not only in indicatinggeneral priorities but also in evaluating theeffects of wide-scale safety campaigns,legislative and/or enforcement changes.

However, as schemes are usua1ly localised,their effects are often difficult to detectamong much larger accident totals. Hence inthe strategy document or Road Safety Plan itwill probably be better to give a summary




listing of the effectiveness of all thelow-cost schemes (see Appendix Aexamples). This is more informative than a single overall figure as it displays the range

of safety efforts taking place and the relativesuccess of the various methods used.


REFERENCES

1. RADIN UMAR R S, G M MACKAY, B L HILLS. Preliminary analysis of motorcycle accidents:short-term impacts of the running headlights campaign andregulation in Malaysia.To be published in J.of Traffic Medicine-1995

2. HAUER E,& P BYER. Bias by selection: the accumcy of an unbiased estimator. Accid-Anal.& Prevention-15, 5, pp323-328-1983.

3. ABBESS C, D JARRETT, C C WRIGHT-Accidents at blackspots: estimating the effectiveness of remedial treatment,with special reference to the ‘regression tomean’ effect. Traffic Engineering & Control, 22 10-1981.

4. WRIGHT C C, C R ABBESS & D F JARRETT. Estimating the regression-to-meaneffect associated with road accident blackspot treatment: towards a more realisticapproach. Accid. Anal.& Prevention. 20, 3, pp199-214, - 1986.

5. MOUNTAIN L,B FAWAZ & L SINENG. The assessment of changes in accident frequencies on link segments: a comparison of four methods.Traffic Engineering &Control, 33, 7 -1992.

6. BOYLE, A J & C C WRIGHT. Accident migration after remedial treatment at accident blackspots. Traffic Engineering & Control, 25, 5 -1984.

7. PERSAUD, B.Migration of accident risk after remedial treatment at accidentblackspots. Traffic Engineering & Control, 28,1-1987.

8. MOUNTAIN L, & B FAWAZ. The effects of engineering measures on safety atadjacent sites. Traffic Engineering & Control, 33, 1-1992

9. ADAMS J. Risk and freedom:the record of road safety regulation. Transport Publishing Projects. Cardiff -1985.

10. TRIMPOP R M, & G J S WILDE Challenges to accident prevention: the issue ofrisk compensation behaviour. STYX Publications, Postbus 2659, 9704 CR Groningen, The Netherlands -1994.



Summary Of Chapter I - INTRODUCTION

The main points covered in this chapter canbe summarised as follows:

Road accidents are a serious problem in Malaysia with more thanone person in every 450 of thepopulation suffering injury or deathon the road each year.

This Guide focuses on theEngineering aspects of improvingsafety.

The Guide also concentrates on theaccident reduction approach(although the priciples applied indevising colinsermeasures also be adopted at the design stage in orderto prevent accidents)

The four basic strategies for reducing accidents are:

-Single sites/blackspots-Mass action schemes-Route action plans-Area-wide schemes

The national casualty reduction targets should be disaggregated tothe local level, and a planned givingdetails of how they will be met, andreporting progress/success.

An annual Road Safety Plan shouldbe produced by all road authoritiesto include a local accident analysis,statement of the targets, givingdetails of how they will be met, andreporting progress/success.

Summary Of Chapter II- ACCIDENT DATABASE

Maintenance of a reliable accidentdatabase is m essential element ofsafety work since it constitutes thebase measure used to:

i) identify the nature and location ofproblems, and

ii) to monitor the effects of remedialaction taken.

Accident Investigation Units shouldbe set up in all road authorities withone full-time staff per 400-1000accidents per year.

The data originates with the Policebut the responsibilities of variousauthorities are summarised below:-

Balai Police- Attend scene of accident and record

details- Enter basic details in 24.hour incident

report book- Open investigation file (for all injury and

some damage-only accidents)- Complete POL27 form

Output:- Main copy of POL27 to HQ- Pages 4 & 15 copies to District JKR/Local

Government Office- Investigation papers for court case

Police HQ-Bukit Aman- Receive POL27 forms, check, and enter

onto mainframe computer- Download data to MAAP files

Output:- Send copy of MAAP files to HPU


CHAPTER VIIISUMMARY



JKR District Office- Produce appropriate scale maps marked

with landmarks.- Check POL27 forms for accident location

on all State & Federal roads- Fill in Section No, 100m distance, map

code, X-Y coordinate coding.

Output:- Completed pages 4 & 15 of POL27 send to

HPU

Local Government Department- Produce appropriate nodal scale maps.- Check POL27 forms for accident location

on all Urban principal and minor roads.- Fill in Node, Link Nos, map code, X-Y

coordinate coding.

Output:- Completed pages 4 & 15 of POL27-send to

HPU

Highway Planning Unit (MOW)- Coordinate all location data - Merge this with data from Police HQ into

MAAP computer files.

Output:- Complete data set copy sent to Police HQ- Appropriate data files made available to all

authorities.

Summary Of Chapter III - INVESTIGATION

Step 1: Identifying And PrioritisingSites

Define a reaction level above whichaction should be taken.

Search data ideally covering aperiod of 3 years using MAAP toproduce initial ranking of sites.These can be:-

- Route action listing in descendingorder of accident totals ( or points)per Section Number per year.

- Single site listing by worst nodesand links, ie. descending order ofaccidents.

- Mass action sites can be rankedaccording to numbers of accidentsof a selected factor (eg. night timeaccidents)

- For Area wide action , residentialareas need to be divided intoapproximately l km squares(though irregular shapes boundedby rail lines, roads, rivers etc. willultimately be used).These areas areusually ranked by numbers ofvulnerable road user accidents.

STEP 2: Preliminary Accident Analysis

Test sites in first listing to ensurehigh accident numbers have notoccurred by chance.

Produce stick diagrams to help lookfor common patterns of accident.

STEP 3: Initial Site Visit

Check plans are up to date.

Visualise accidents on record toconfirm manoeuvres and makepreliminary judgement of causes.

Photograph site.

Classify sites if possible as ‘easy’ or‘hard’.




Summary Of Chapter IV- DIAGNOSIS

STEP 4 Collection Of Further DataAnd Analysis

Study accident data at the site inmore detail including sketchdiagrams, and produce collisiondiagrams.

Classify accidents into types.

Amend stick diagrams to includemy further information and searchfor dominant accident patterns.

Gather any available data such astraffic flow, dates of roadalterations.

Determine likely human factors -any perceptual traps.

STEP 5: Site Studies And Analysis

Make further site visit and look forlikely features which may becontributing to accidents.

Plan the following further studies,as necessary:

- Traffic flow manoeuvre counts.

- Pedestrian road crossing flow in markedroad lengths if relevant.

- Speed measurements on approach tojunctions or bends indication of possibleproblems.

- Take still photographs and/or video as arecord for report, or use to study problembehaviour.

- Conduct traffic conflict study most usefulat junctions to :

i) Supplement accident data,

ii) Help diagnose problems, and

iii) Use in future evaluation of remedialwork implemented.

Summary Of Chapter V- SELECTION

STEP 6 Select PosibbleCountermeasures

A road hierarchy should beestab1ished.

Decide on economic objectivesfor the different scheme types(eg.50% FYRR at single sitesto10-25% area-wide action).

Several treatment proposals fora site should be considered (listsof schemes shown to be effective inseveral countries are given), andeach should:-

- aim to reduce the prevalent accidenttype(s);

- not increase other types of accident at thesite or in the surrounding area;

- not cause undesirable effects on othertraffic movements or on the environment.

For area-wide residential schemes,aim to reduce speeds as opposed torestricting vehicle movements andmaintain good consultation withlocals and the emergency services.

Consider whether schemes need toincorporate road user training andmedia campaigns.




STEP 7: Priortise Treatments & Sites

Estimate costs and benefits of eachtreatment for which the following isrequired:

- capital costs- estimate of benefits- estimate of any disbenefits.

Select most cost-effective solutionin terms of best First Year Rate ofReturn (FYRR) or best Net PresentValue to Present Value Cost ratio(NPV/PVC). Only those schemeswith FYRR > 50% should initiallybe considered.

Draw up list of sites in priorityorder of best NPV/PVC ratio, anddecide on cut-off of sites to betreated within the budget.

Summary Of Chapter VI - IMPLEMENTATION

STEP 8: Detailed Design AndInstallation

Carry out a road safety audit at thedesign stage and immediately beforeopening to traffic.

Ensure adequate safety standards arefollowed at the safety improvementconstruction site.

Maintain a 1og of dates of the worksand of actual costs.

Summary Of Chapter VII - EVALUATION

STEP 9: Monitoring

The importance of monitoring after schemeimplementation is stressed.

Monitoring should be carried out atdifferent levels: for the whole areacovered by the road authority;immediately after each individualscheme; and for longer termconclusions.

Variables other than accidentfrequency can be used to monitorthe effectiveness, particularly inrelation to the objectives of theparticular countermeasure. A seriesof other factors are stronglyrecommended for area-wideschemes.

It is important to monitor othersurrounding areas which could beaffected by the scheme and toidentify as large a group of controlsites as possible of similar naturebut well away from the study sites.

STEP 10: Evaluation

Remedial action schemes should beevaluated so that knowledge can be gainedabout relative performances. This will assistdecision making on efficient allocation ofresources in the future.

Statistical tests should be used inbefore and after studies to compareaccident changes at the treated siteswith the control sites.

The investigator should makeallowance for the known otherfactors that can affect the estimateof the effect of the measure onaccidents (eg. regression-to-mean).

As a guide to overall effectivenessof a road authority’s road safetyprogramme, a summary list ofindividual schemes, grouped in anappropriate manner, should beproduced and included in the RoadSafety Plan document.




This Appendix contains extracts from recent road safety strategy documents or Road SafetyPlans of two highway authorities in the United Kingdom, ie. Doncaster MetropolitanBorough Council and Berkshire County Council. They are included as examples only of theformat and type of information which, it is recommended, be incorporated in similarpublished documents in Malaysia.

Road Safety Plans are now produced annually by most road authorities in the UnitedKingdom regardless of the current success or failure of each in achieving its target. Theyserve as a means of ensuring that the road authority concentrates on managing its particularproblems effectively, and provide the public and higher authorities with a valuable record ofthe efforts it is making on their behalf towards improving the safety of the road network.

It should be noted that Berkshire County Council, having responsibility for a larger roadnetwork, have now appointed a commercial highways and planning consultants, the BabtieGroup, to carry out the task of producing their Plan.


APPENDIX AExample of Road Safety Plans




2.0 PROGRESS TOWARDS TARGET

Berkshire ProgressIn 1989 when the County Council adopted the casualty reduction target, some 4354casualties had resulted from accidents on Berkshire’s roads. In order to achieve the targetreduction of one third of the average 1981-85 figure by the year 2000, this figure mustreduced to 2847. Progress towards the target is shown opposite. Whilst casualty numberscontinue to decline it can be seen that an increased rate of reduction is now required if theobjective is to be achieved.

National ProgressFor comparison purpose the national progress towards the year 2000 target is also shownopposite. It can be seen performance in Berkshire is better than the national average.It can be seen that both the Berkshire and National trends show the same effect: an early andrelatively rapid reduction as the “easier” sites are tackled, followed by a levelling off asmore difficult problems (often related to behaviour as much as to the road layout) have to betackled.

WHILST CASUALTY NUMBERS CONTINUE TO DECLINE, MORE SIGNIFICANTREDUCTIONS ARE REQUIRED TO MEET THE YEAR 2000 TARGET




3.0 ACCIDENT TRENDS AND ANALYSIS

An analysis of accident trends has shown that speeding particularly in urban areas continuesto be a major factor in accident causation. The young and inexperienced road users featurepredominantly in Berkshire's accident statistics, and the fact that two-thirds of all casualtiesresulting from accidents on Berkshire's roads are the drivers and passengers of cars is acause for concern. It is at these key areas that resources must be targeted if the year 2000targets is to be met.

The Size Of The ProblemThroughout 1993 on roads in Berkshire there was a total of 2773 accidents involvingpersonal injury.

These resulted in 3672 casualties of which:

33 were fatal347 were serious injuries 3292 were slight injuries

The total number of fatalities and serious injuries has declined every year since 1989 andnow represents a 65% reduction over the 1981 - 85 average figure.




The only specific road user group showing and increasing casualties trend is that of caroccupants. Casualty levels in this group are currently 10% higher than the 1981-85 average.

It is clear that this casualty group holds the key to achieving the casualty reduction targetand the County Council's objective in the next few years will be to reduce casualties in thisarea.

THE KEY TO ACHIEVING THE YEAR 2000 TARGET WILL BE REDUCE TO REDUCECASUALITIES IN THE CAR OCCUPANT ROAD USER GROUP




Accidents Locatios In BerkshireAs can be seen in the figures below, the majority of accidents in Berkshire take place onurban roads. (i.e. those roads subject to a speed limit of 40mph or less). It is evident that ifthe casualty reduction target is to be met then a significant proportion of engineeringprogrammes and police enforcement activity must be focused on these areas.

THE COUNTY COUNCIL WILL CONTINUE TO FOCUS ROAD SAFETY RESOURCESTOWARDS ACCIDENT CONCENTRATIONS, PARTICULARLY THOSE IN URBAN AREAS

Vulnerable Road User Groups In BerkshireThe distribution of road traffic casualties by age and road user class shows thatinexperienced users of each mode are more likely to be involved in accidents. This isparticularly evident with the young car driver since accident records show that overone-third of all accidents involve drivers in the 17 to 24 age range.




As discussed in later sections, Education Training and Publicity initiatives are directedprincipally at these inexperienced and hence vulnerable groups.

SpeedSpeeding by drivers and riders is the most common contributory factor to deaths and injurieson Berkshire's roads.

A study by the Transport Research Laboratory (TRL) has indicated that between 22 and 32percent of the accidents studied had excessive speed as a contributory factor.

In terms of the 1993 injury road accident figures for Berkshire, this would indicate thatspeeding had been involved in over 800 injury road accidents.

As discussed in later sections, the theme of excessive speed and road safety will play amajor part in the County Council's engineering and education programmes and in theenforcement activity of Thames Valley Police.

AN ANALYSIS BY TRL INDICATES THAT A REDUCTION INAVERAGE SPEED EVERYWHERE OF THE ORDER OF 1 KPH COULD SAVE 5

PERCENT OF ALL INJURY ACCIDENTS




4.0 ENGINEERING ACTION

The great majority of schemes in the County Council's highway works programme willresult in road safety improvements. Indeed the Council's scheme selection procedures areheavily biased towards tackling sites with a persistent injury accident problem.

In recognising the importance of reducing the level of accidents on the County's roads theGovernment allows Supplementary Credit Approval (SCA) to be claimed againstengineering projects which can demonstrate potential injury accident savings. Hence it is inthe County's interest to promote such schemes above those to which no potential injuryaccident savings can be ascribed. Recent engineering road safety initiatives are listed below:

TRAFFIC CALMING has continued to be heavily promoted within Berkshire withnumerous projects including 20mph zones, chicanes, road narrowings, road humps and mini roundabouts being installed around the County.

In recognition of the accidents caused through excessive speed by drivers and ridersin urban areas, Berkshire County Council quickly responded to the regulationsissued in 1992 by installing the first 22 fixed speed camera sites in Berkshire. Thiswork will continue in 1994/95 with a further 50 sites planned and complements redlight enforcement cameras already installed.

The first non-trunk road variable speed limit scheme in the country was introducedin Slough.

The first Berkshire Toucan crossing is being progressed in Newbury.

Berkshire’s 3rd Puffin crossing is being progressed in Thatcham.

Appendix A lists local safety engineering schemes planned for 1994/95 together withcomment on their estimated effect on injury accidents over a three year period. As canbe seen considerable emphasis will continue to be placed on tackling the problems ofspeeding in urban area with many speed camera and traffic calming schemes programmed atidentified high risk accident sites. Such schemes are seen as one of the prime accidentreduction measures currently being implemented in Berkshire and are expected to make amajor contribution towards changing attitudes to inappropriate speeds.

The County Council carries out a continuous programme of investigation of accidentpatterns at High Risk Sites. Potential schemes arising from this process are presented toMembers for funding consideration

The potential for reducing accidents will continue to be taken into account when deciding onthe priorities for traffic management works promoted by the Area Highway Sections.

Appendix B lists all High Risk sites in Berkshire with comment on action already taken orproposed.




A minimum of 100 sites will be investigated in depth in 1994/95 either as individual sites oras part of an area wide or route approach. In addition to this, accident investigation willcontinue to feature predominantly in the County Council's continuing programme of AreaTraffic and Transport Studies.

The County Council continues to monitor its success in accident remedial work to ensure acost effective approach to the work. Indeed, this feedback is essential to maintain levels ofexpertise in this rapidly developing field. Appendix C gives before and after information andclearly demonstrates the cost effectiveness of this work.

The County Council continues to improve road safety through its close control ofdevelopment proposals and liaison with the local Planning Authorities. Every opportunitywill be taken to resolve existing road safety problems or prevent others arising as a result ofnew development. Developer contributions will also be actively sought to enable positiveaccident prevention and remedial work to be pursued at identified problem sites.

CONSIDERABLE EMPHASIS WILL CONTINUE TO BEPLACED ON TACKLING THE PROBLEM OF SPEEDING IN VRBANAREAS AT

IDENTIFIED HIGH RISKACCIDENT SITES.




APPENDIX BPOL27 Accident Report Form




APPENDIX CPoisson Probabilities (Single Factor Values)




APPENDIX DChi-squared Table




APPENDIX EStandard Symbol For Collision Diagrams




APPENDIX FDiscount Factor Tables



COMPARISON OF MEAN SPEEDMEASUREMENTS

To determine whether the mean speedof one set of speed measurements issignificantly different from another (ie.between a “before” and “after” study),it is necessary to determine the means andstandard deviation of the difference inmeans.

Let b1,b2..................bnb the before speedreadings

and a1,a2,..............ana be the after speedreadings

we then ca1culate the equations below:

Having found the value of t we look atthe table over page with (na+nb- 2) degreesof freedom. If the value of t exceeds that forthe 5% level (the t =0.05column) we can be95% conndent that the true mean speed haschanged.


APPENDIX GComparison Of Mean Speed Measurements and T-Distribution Table

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