quarter 3 2016 issue 4 : overload control … 3 2016 issue 4 : overload control solutions ......

T H E O P E R A T O R O F C H O I C E

INTERTOLL AFRICA (PTY) LTD, 9 COUNTRY ESTATE DRIVE, WATERFALL BUSINESS ESTATE, JUKSKEI VIEW, 1662, SOUTH AFRICA www.intertoll.co.za

NEWSLETTER 4 QUARTER 3 2016 ISSUE 4 : OVERLOAD CONTROL SOLUTIONS

EDITORIALWelcome to the next quarterly edition of Intertoll Africa’s Newsletter!

Please note our newly redesigned website is now available on www.intertoll.co.za and contains a wealth of information on our products and services.

As an integrated Operator and Developer with more than 30 years of experience, Intertoll Africa wishes to highlight the importance of controlling the overloading of vehicles on the road infrastructure. As will be illustrated in this article, the process of implementing and enforcing effective vehicle overloading controls will pay handsome dividends in prolonging the life of a country’s road infrastructure and reducing the road rehabilitation and maintenance costs.

Editor: Laurent Bouchacourt eMail: [email protected]

INTRODUCTION

Roads are the most important transport communication medium in Africa and are used by almost everyone on a daily basis. Despite the fact that roads are provided for the benefit of the road user, they also play a significant role in promoting economic growth and improving the living standards of the general population.

Worldwide research shows that damage to a road by axle loads exceeding the legal limit, increases exponentially with the increase of the load above the designed axle load: for example, an axle carrying double the legal load may cause from 4 to 60 times as much damage as one legal axle load, depending on the condition of the vehicle, and condition and type of road. In South Africa, where overload control measures are enforced on most major roads, it is estimated that between 15 and 20% of all heavy vehicles travelling on the roads are still overloaded.

PAVEMENT DESIGN PRINCIPLES

The aim of a structured design for a road pavement is to produce a balanced road pavement design which, at minimum present worth of cost, will carry the traffic for the structural design period in the prevailing environment, at an acceptable service level without major structural distress. If necessary, the pavement should be capable of being strengthened by various rehabilitation measures to carry the traffic over the full analysis period, usually set at twenty (20) years.

The typical elements of the road pavement layers are shown in the figure enclosed to illustrate some of the terms used in road pavement design.

Although the bearing capacity of a pavement is considered to be constant, different traffic spectrums will have different damaging effects on the pavement due to the different axle-load compositions of the traffic spectrums. In order to standardise the design loads for the road pavement, the cumulative damaging effect of all individual axle loads (i.e. traffic spectrum) is expressed as (or converted to) the number of Equivalent Standard single-Axle loads (ESAs).

The pavement design strategy will influence the total cost of a pavement structure. In order to fulfil the design objective of selecting the optimum pavement in terms of present worth of cost, it is necessary to consider how the pavement is expected to perform over the entire analysis

Pavement Structure Terminology


INTERTOLL AFRICA (PTY) LTD, 9 COUNTRY ESTATE DRIVE, WATERFALL BUSINESS ESTATE, JUKSKEI VIEW, 1662, SOUTH AFRICA www.intertoll.co.za2

NEWSLETTER 4 - QUARTER 3 2016 : OVERLOAD CONTROL SOLUTIONS

* If surfacing is not maintained and if water susceptible materials are used in the pavement.

Figure 1: Design 1 - Two Resurfacings and One Rehabilitation In Analysis Period

period. The manner in which a design strategy can be presented is demonstrated schematically in the figures below, which show the generalised trends of riding quality decreasing with time, and traffic for two different pavement structures, namely:

Design 1, which requires resurfacing to maintain the surface in a good condition, and later some structural rehabilitation such as an overlay (Figure 1); and

Design 2, which is structurally adequate for the whole of the analysis period and requires only three resurfacings (Figure 2).

* If surfacing is not maintained and if water susceptible materials are used in the pavement.

Figure 2: Design 2 - Three Resurfacings and No Rehabilitation In Analysis Period

The number of ESAs is termed the equivalent traffic. The load-equivalency factor relates the number of repetitions of a given axle load to the equivalent number of ESAs.

This equivalency factor is a function of pavement composition, material types, definition of terminal conditions and road or street rideability and the condition (particularly that of the vehicle suspension) of the vehicles.

Average equivalency factors (F) for a relative damage exponent is based on the load equivalency formulae:

Where: F = load equivalency factor, P = axle load in kN, and n = relative damage exponent.

Research has shown that a relative damage exponent value of 4.2 can be applied to most general pavement designs. However, pavements that are sensitive to overloading, such as shallow-structured pavements with thin cemented bases, may have (n) values of more than 4.2 whereas less sensitive, deep-structured pavements may have (n) values of less than 4.2.

While research has shown that light vehicles such as cars and light commercial vehicles, make a relatively small contribution to the structural damage of a road pavement, it has been estimated that 60% of the damage to the road network in South Africa is caused by illegally overloaded heavy vehicles.

THE REAL IMPACT OF OVERLOADED HEAVY VEHICLES

Relationship between load mass per axle and damaging effect on wearing course




Based on the equivalency principle, a vehicle has an axle that is overloaded by just 25% (i.e. the axle load is increased from 80kN to 100kN in our example) the axle passage along the road is equivalent to 2.4 axles. The following calculation illustrates the effect of this overload on the life of the road.

Consider a road category ES10 designed for 10 million E80 ESAs over a 20 year life span, the Annual Average Daily Equivalent Traffic (AADE) is:

10 000 000/20/365 = 1 370 axles assuming no annual traffic growth.

If 15% of the vehicles are overloaded by 25%, as discussed above, the AADE is effectively:

1370 (1-0.15) + 1370(0.15) x 2.4 = 1 658 axles and the effective design life of the road is:

10 000 000/1658/365 = 16.5 years.

It was noted, some years ago, during an Intertoll project in Bangladesh, where there was no “official” overload control enforcement and gross overloading of vehicles was endemic, that some vehicles with a single rear axle were carrying loads that increased the rear axle mass to 25tonnes, i.e. an overload of 250%. This one vehicle was effectively equivalent to more than 50 “normal” vehicles! Table 1 below seeks to illustrate the actual impact of good, poor, or no overload controls on the design life of a road.

Table 1: Illustrative Effect of Vehicle Overloading on Road Pavement Life

Overloaded Trucks

Damage to Vehicles and Structures Caused by Overloading

OVERLOAD CONTROL PRINCIPLES AND BEST PRACTICES

In order to implement effective control of vehicle overloading, it is necessary that a sound foundation of heavy vehicle transport regulations, legislation, enforcement practices, and maintenance regimes are implemented.

The regulations surrounding the transport of goods by heavy vehicle and the permissible single axle and multiple axle loads, gross (overall) weight of the vehicle configuration, lengths of vehicles, dimensions of vehicles and loads, securing of loads, types of loads (hazardous, non-hazardous), marking of vehicles and loads, etc. need to be published so that they can be implemented and enforced. Regulations within an economic group of




countries and between neighbouring countries should, as far as possible, be consistent, as it will make enforcement and the loading of the trucks that travel across the country’s boarders easier, particularly if the country of origin of the vehicle has a higher allowable axle load than the destination country.

Legislation enforcing the regulations surrounding the transport of goods by heavy vehicle must be clearly framed and enforceable, define enforcement authorities and enforcement methods, and define stringent terms for the payment of fines and the redistribution of loads before the release of the vehicle, which was overloaded but is now compliant, back onto the roads to proceed with its journey. In addition, the penalties associated with overloading of a vehicle must impose a significant financial and time delay punishment on the truck operator and the vehicle must be impounded in a secure area and not released until all the fines have been paid and the excess load has been redistributed to other vehicles.

A network of fixed weigh stations must be placed at strategic locations along the major truck corridors such that the majority of the truck traffic is weighed and monitored and mobile weighbridges that can be moved quickly from one location to another. This random pattern should include different and irregular location of the monitoring points so that no predictable pattern for the mobile monitoring activities can be determined. Enforcement authorities, the enforcement procedures, and the enforcement practices must be monitored, be auditable, and be framed in such a manner that bribery of enforcement officials is minimal and quickly found and controlled - one of the benefits of partnering with a Private Operator (‘checks and balances’).

Furthermore, overloaded vehicles become a traffic hazard, especially regarding the heavy vehicle’s braking system and the additional braking distance involved. On steep uphill gradients where no climbing lane is provided, the slow moving heavy vehicles cause traffic disruption and frustration amongst the light vehicle drivers.

ROUTINE ROAD MAINTENANCE: A KEY COMPONENT OF OVERLOAD CONTROL MANAGEMENT

Because of the limited funds available for the construction of new roads, it is essential that effective campaign to maintain the road infrastructure be implemented. Therefore, Routine Road Maintenance (RRM) must be carried out continually to control vegetation along the road, clean side drains and culverts, repair shoulder breaks, re-gravel and grade gravel shoulders, repair damage to the road furniture, seal cracks in the road surfacing (to prevent water penetration into the pavement layers), repair potholes, and repaint road markings in order to prolong the useful life of a road. Furthermore, the implementation of a Pavement Management System (PMS) with suitable axle weight monitoring stations and traffic counting stations to provide appropriate inputs into the PMS is highly recommended.

OVERLOAD CONTROL TECHNOLOGIES

The enforcement of the regulations and legislation surrounding the transport of goods by heavy vehicle and the permissible single axle, multiple axle loads, and gross weight of the vehicle permitted, is usually carried-out using a scale. Traditionally, these are static weighbridges with multiple platforms to be able to weigh the individual axles and axle groups of the vehicle plus determine the gross weight of the vehicle whilst the vehicle is stationary. This type of weighbridge will typically have an accuracy of about 1%, provided it is correctly calibrated and maintained.

Enforcement activities must also be accompanied by an ongoing information and public relations campaign between the Roads Authorities, the road users and truck Operators.




Multiplatform Static Weighbridge

Vehicles can also be weighed dynamically, or whilst they are in motion. With the advent of electronics and the advances in technology, this equipment for weighing vehicles in motion has become more accurate and compact. Weigh-In-Motion (WIM) scales are classified into two general types, namely High Speed Weigh-In-Motion (HSWIM) scales and Low Speed Weigh-In-Motion (LSWIM) scales.

The HSWIM is used in “open road” situations to weigh vehicles at high speed (between 60kph and 130kph). On a straight section of road with a vertical grade of less than 2% and a “smooth” surface free from irregularities, where the vehicles are travelling at a constant speed, weight accuracies of between 8% and 10% can be readily obtained.

HSWIM with “Strain Plate” Weighing Sensors

The LSWIM is used in “screening” situations to weigh vehicles at low speed (between 3kph and 5kph), Because of the slow speeds involved, LSWIM weighing activities are usually conducted in diversion lanes adjacent to the road. On a section of road with a vertical grade of less than 1% and a “smooth” surface free from irregularities, where the vehicles can travel at a constant speed, weight accuracies of between 3% and 5% can be readily obtained. Depending on the load cells used for the weighing scales, vehicles can also be weighed statically on these scales one axle at a time. Because of the increased accuracy of this type of WIM scale, it is possible to assize them and use them as certified scales for enforcement purposes.

As stated previously, fixed weigh stations are usually located alongside the road and HSWIM stations monitor the approaching traffic and signal vehicles that are over certain weight tolerances to be diverted into the weigh stations for more accurate weighing. Vehicles that are signalled to divert and disobey this signal are monitored by Automatic Number Plate Recognition (ANPR) CCTV camera systems that signal traffic officers to apprehend the vehicle and escort it back to the weigh station.

Typical LSWIM Installation




Mobile Weigh Equipment

THE BENEFITS OF A PUBLIC-PRIVATE PARTNERING APPROACH TO THE OPERATION & MAINTENANCE OF WEIGH STATIONS

Once effective enforcement of overload control has been implemented, it is essential that weigh stations are effectively operated. and maintained – ideally, through a cooperation between the enforcement authority issuing fines and impounding vehicles – typically, the police or “gendarmerie” – and a Private Operator collecting the fines on behalf of the Road Fund and managing the day-to-day operations of the facilities . Whilst it may not be “economical”, certain “key” weigh stations on a road network should be operated on a 24hour per day, 365 day per year schedule as a deterrent to truck operators using the night-time hours and week-end days to move overloaded vehicles certain in the knowledge that they will not be subjected to checking. Thus, overload enforcement should be continued with the road infrastructure development of the country.

After weighing, overloaded vehicles are diverted into a holding area where the excess load must be redistributed to another vehicle, all overloading fines and charges must be paid, and impounding timeouts, if any, served, before the vehicle is allowed to proceed.

It has been found in some countries, particularly where the funds for additional road infrastructure development are loaned, that the provision and operation of weigh stations and the routine maintenance of the road is a condition of the loan or grant. These operations are ideally suited for private organisations in co-operation with the statutory body responsible for overload law enforcement of weigh stations. The operation and maintenance becomes more effective when the road infrastructure is also tolled to contribute to the cost of road maintenance, in addition to the overload control measures. Overload control systems and infrastructure can also be implemented and financed effectively through Public Private Partnerships (PPPs) where the Private Operator also acts as the Developer / Funder of the project and pays a Royalty to the Authorities.

CONCLUSION

The points raised in this article are indicative guidelines to stakeholders, such as Ministries of Public Works or Transport, Road Funds and Authorities, or Overload Enforcement Authorities, in determining the most appropriate mix of Overload Control Methods, based on a set of key parameters central to the definition of a robust, long-lasting and effective Overload Control strategy and solution. Some overload control stations have already set an excellent benchmark on the Continent – such as the Atakpamé overload control center in Togo – and must be celebrated.

Atakpamé Weigh Station (Togo)




Intertoll, as an Integrated route operator and Developer with extensive experience in the provision of infrastructure through PPPs, tolling operations and maintenance, overload control, and Routine Road Maintenance is ideally suited to partner with Road Authorities to plan, equip, operate, finance and maintain overload control, tolling, and Routine Road Maintenance activities.

The importance of applying effective Overloading Control and Enforcement measures to protect the road infrastructure against this endemic practice by heavy vehicle operators cannot be overemphasised. Table 1 clearly illustrates the catastrophic effects of uncontrolled overloading of heavy vehicles on a road pavement. Partnerships between the Enforcing Authorities / Road Agencies and Private Operators can yield very positive outcomes.

For more information please contact:

Malcolm ElsworthToll System Design ManagerTelephone: +27 10 060 2054Email: [email protected]

Laurent BouchacourtDirector: Project DevelopmentTelephone: +27 10 060 2091Email: [email protected]

IN OUR NEXT ISSUE...

In our next Quarter 4 2016 issue, we will unpack how Intertoll Africa can bring enhance the capacity of Road Agencies and Road Funds in managing Routine Road Maintenance (RRM) jointly and we will offer you an opportunity to be the first ones to test our new Temporary Collection Toll Plaza on one of your roads. (see: www.intertoll.co.za/products-intertoll.php)

quarter 3 2016 issue 4 : overload control … 3 2016 issue 4 : overload control solutions ......

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