manual of traffic i 00 dey s

7/29/2019 Manual of Traffic i 00 Dey s

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SCHOOL OF51 CIVIL ENGINEERING

INDIANADEPARTMENT OF TRANSPORTATION

Joint Highway Research ProjectDraft ReportManual of Traffic ImpactStudiesSoumya S. Dey and Jon D. FrickerFHWA/IN/JHRP - 92/5

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UNIVERSITY


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Joint Highway Research ProjectDraft ReportManual of Traffic ImpactStudiesSoumya S. Dey and Jon D. FrickerFHWA/IN/JHRP - 92/5


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Draft

MANUAL OF TRAFFIC IMPACT STUDIES

Soumya S . DeyGraduate Research Assistant

Jon D. FrickerAssociate Professor of Transportation Engineering

Joint Highway Research ProjectProject No.: HPR-2039 (029)

File No. : 3-5-10

Prepared as a part of an InvestigationConducted by

Joint Highway Research ProjectEngineering Experiment StationPurdue University

in cooperation with the

Indiana Department of Transportation

and the

U.S. Department of TransportationFederal Highway Administration

Purdue UniversityWest Lafayette, IN 47907February, 1992


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Digitized by the Internet Archivein 2011 with funding from

LYRASIS members and Sloan Foundation; Indiana Department of Transportation

http://www.archive.org/details/manualoftrafficiOOdeys


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TABLE OF CONTENTS

Page

LIST OF EXHIBITS iiiFOREWORD ivCHAPTER I . INTRODUCTION 1CHAPTER II . STUDY PROCEDURE 5CHAPTER III . PRELIMINARY STUDY 8CHAPTER IV. WARRANTS FOR A COMPLETE TIA 11CHAPTER V. TRAFFIC OPERATIONS ANALYSIS 13CHAPTER VI . INITIAL MEETING 15CHAPTER VII. PREPARER AND REVIEWERQUALIFICATIONS 2 2CHAPTER VIII. NON-SITE TRAFFIC ESTIMATE 23CHAPTER IX. TRIP GENERATION 27CHAPTER X. TRIP DISTRIBUTION 32CHAPTER XI . TRAFFIC ASSIGNMENT 3 6CHAPTER XII . PASS-BY TRIPS 37CHAPTER XIII . MIXED-USE DEVELOPMENTS 41CHAPTER XIV. ANALYSIS 42CHAPTER XV. CONCLUSIONS AND RECOMMENDATIONS 49CHAPTER XVI . REPORT 53CHAPTER XVI . STAFF REVIEW 56


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Page

BIBLIOGRAPHY 58APPENDIX A. PRELIMINARY STUDY REPORT OUTLINE 61APPENDIX B. INITIAL MEETING CHECKLIST 63APPENDIX C. SAMPLE REPORT OUTLINE 68


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LIST OF EXHIBITS

PageFigure 2.1 Flowchart Showing the TrafficImpact Study Procedure 7Table 3.1 Preliminary Warrants for TrafficImpact Analysis 9Table 6.1 Typical Data Collection and FieldReconnaissance Items 2Table 6.2 Typical Background Data Needed for aComplete Traffic Impact Study 21Figure 12.1 Schematic Diagram Showing Primary,Pass-by and Diverted Linked Trips 38Table 15.1 Transportation Demand ManagementTechniques With Potential to ReduceSite Traffic Generation 51Table 16.1 Typical Exhibits in a DetailedTraffic Impact Study 55


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IV

FOREWORD

This manual, entitled "Manual of Traffic Impact Studies",is a product of an HPR study called "Guidelines for TrafficImpact Analysis of Developments Along State Highways". Thestudy was conducted by the Joint Highway Research Project(JHRP) in the School of Civil Engineering at Purdue Universityin conjunction with the Indiana Department of Transportation(INDOT) and the Federal Highway Administration (FHWA)

.

At the time the study was undertaken, a need was iden-tified to establish a standardized procedure or guidelines forrequesting, preparing and/or reviewing a traffic impact studyfor a proposed development that would affect state highways.Cases of rezoning and building permits were handled at thelocal level (city or county) , each of which had their ownguidelines for such studies, if any. INDOT handled newdevelopments when access driveway permits were necessary.Often, INDOT is not involved in the transportation aspects ofa site's development until access permits are requested foraccess to state routes. This can occur too late in thedevelopment's construction for any traffic-related problem tobe remedied as effectively and economically as they could havebeen in the planning stage. Also the need for greater coordi-nation between the INDOT and the local agencies in this matterwas felt.

This manual is a first step in this direction. It isdesigned to be compatible with the Applicant's Guide andProcedure Manual for Transportation Impact Studies forProposed Development for the City of Indianapolis [21,22].


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The ideas and concepts in this manual borrow from thecomposite experience and effective procedures of numerousagencies and practitioners. It also incorporates, and in somecases enlarges and adjusts upon, accepted procedures asdocumented in other standard references, especially:

ITE Recommended Practice- Traffic Access and ImpactStudies for Site Development [1]

Transportation and Land Development [2] Site Impact Traffic Evaluation Handbook [3]

ITE Trip Generation [5]

The manual also recognizes that traffic impact analysisis a site-specific issue that can depend on many variableslike the amount and type of data available and certain otherlocational parameters. Instead of prescribing a specificprocedure for every step, it gives, in most of the cases,various options to obtain specific results. Therefore, itallows enough flexibility to the study preparer to useinnovative methods based on sound engineering judgment.However, this should be done with the prior consent of thestudy reviewer (s)

.

The study Advisory Committee assisting in the preparationof the manual comprised of:

R. Cales (INDOT) M. Newland (INDOT) J. Poturalski (INDOT) E. Ratulowski (FHWA) C. Venable (INDOT)


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VI

Input is expected from a panel of consultants, developersand local government officials before the final draft of themanual is prepared.


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CHAPTER IIMTRODUCTION

One of the fundamental aspects of transportation planningis the interdependency of land use and transportation. Thepattern of land use is affected by the level of accessibilityprovided by the existing transportation system. Any newdevelopment leads to the production and/or attraction of tripsand thus creates new travel demands. Hence there is a need forimprovement of the existing transportation facilities either in the form of new infrastructure or in the form ofimproved operational conditions. Such improvements, in turn,make the land more accessible to the existing activity centersand the attractiveness of the land increases. This spurs newdevelopments, and the cycle starts again. This processcontinues until some kind of equilibrium is attained.

In the short-run, however, the predominant influence isthat of land use on transportation [24]. Consequently, thereis a need for a standardized methodology to assess the infra-structure or operational improvements needed for the trans-portation system.

Traffic Impact Analysis (TIA) is a specialized study ofthe impact that a given type and size of new land use has onthe nearby transportation system.

One of the major transportation issues addressed in the1980' s has been the growing concern about the transportation


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infrastructure not being able to keep pace with development.This imbalance between transportation supply and demand hasresulted in congestion, delay and safety hazards at manylocations throughout the country. As a result, traffic impactanalysis is becoming more popular as a planning tool so thateffective mitigating measures can be taken in advance. Infact, in some regions, a traffic impact study is mandatory forany developments larger than a few single family dwellingunits.

PURPOSE OF TRAFFIC IMPACT ANALYSIS

The main purpose of traffic impact analysis are [22]:

1) To ascertain the operational conditions on theadjacent roadway network when a proposed development isaccommodated within the existing transportation infrastructurealong with other proposed developments (as reflected in theComprehensive Development Plan)

.

2) To identify transportation improvements required tomaintain the existing operational conditions.

3) To determine whether access to the proposed develop-ment will hamper traffic operations and safety near the site.

4) To identify present or future transportation systemdeficiencies without the new development.

5) To provide decision makers with a basis for assessingthe transportation implications of approving proposed zoningchanges and development applications.

7) To provide a basis for estimating the cost of proposedmitigating measures. Consequently, a traffic impact study can


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be used to determine the "fair share" of the improvement costto be paid by the developer.

PURPOSE OF THE MANUAL

This manual is intended to establish a standard method-ology for traffic impact analysis. This would result inconsistency in study requests, preparation and review. Such astandardized procedure would be beneficial to everyoneinvolved in the development process. First and foremost, themanual will take the study preparer through a step-by-stepprocedure and enable him to present the study findings andrecommendations in a systematic manner consistent with thereviewer's expectations. Second, it will enable reviewers toreview the study in a systematic manner. Finally, it willpromote understanding and awareness of transportation relatedissues among those involved in the development procedure.

The manual is not intended to make things more compli-cated and time-consuming. On the contrary, in the long-run, asthe assumptions and procedures become accepted practice, thetime involved in the process will decrease for both parties.

ORGANIZATION OF THE MANUAL

The manual is organized into small chapters, each corre-sponding to an important activity in the study process.

Chapter 1 provides an overview of traffic impact analy-sis.

Chapter 2 describes the different steps involved in theproposed traffic impact analysis methodology.

Chapter 3 describes the preliminary study process.


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Chapter 4 describes the warrants for a complete trafficimpact study.

Chapter 5 contains the warrants and analysis required foran operations analysis.

Chapter 6 deals with the topics to be addressed in theinitial meeting between the study preparer and reviewer (s).

Chapter 7 describes reviewer and preparer qualifications.

Chapter 8 discusses methods of estimating non-sitetraffic in the horizon year.

Chapters 9, 10 and 11 give methods of trip generation,trip distribution, and traffic assignment, respectively.

Chapters 12 and 13 describe how to handle pass-by tripsand make adjustments for mixed-use developments.

Chapter 13 gives the analysis involved in the studyprocess.

Chapter 14 describes the study findings and recommenda-tions.

Chapter 15 gives guidelines about report format.

Chapter 16 describes the staff review process.


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CHAPTER II

STUDY PROCEDURE

Typically a traffic impact study (TIS) should be con-sidered in conjunction with an application for approval of anyof the following [1,28]:

zoning changes subdivision/platting site plan building permit driveway (access) permit comprehensive plan amendments requested by thedeveloper

However, INDOT gets involved in the traffic impactanalysis procedure only when access permits are requested fordriveway access to state highways.

The proposed methodology of traffic impact analysis willbe a one-, two-, three-, or four-step process depending on thetype of development under consideration. The different stagesof a traffic impact study procedure are discussed below.

Step 1. A preliminary study will be required of alldevelopments meeting certain "preliminary warrants". These arediscussed in Chapter 3 of the manual. If the development underconsideration does not satisfy the preliminary warrants, nofurther study is required and the TIA procedure stops here.


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Step 2. From the findings of the preliminary study itwill be decided if the "warrants for a complete TIA" (Chapter4) are met. If the warrants are satisfied then a detailedtraffic impact analysis (discussed in Chapters 8 through 15)will be required for the development. If the warrants are notsatisfied, go to Step 3, otherwise go to Step 4.

Step 3 . This step involves determining whether thewarrants of an operations analysis are met. If the warrantsare met, then an operations analysis has to be conducted(Chapter 5) . If the warrants for operations analysis are notmet, the study procedure stops here. Else go to step 4.

Step 4. This involves the staff review (Chapter 16) ofthe traffic operations analysis or the traffic impact analy-sis. If the study is satisfactory, the process stops here.Else, the revisions suggested have to be incorporated and sendback for further review. This is the last step of the studyprocess.

Figure 2.1 is a flowchart showing the different stages ofa traffic impact study.


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c PROPOSED DEVELOPNE NT J

DOES IT MEET PRELIMINARYWARRANTS'?

YES NO

c PRELIMINARY STUDY

f INITIAL MEETING \

J NO TIAREQUIRED(STOP)

DOES IT MEE1WARRANTS'?

NO YES

c STOPCONDUCT TRAFFIC

^OPERATIONS ANALYSISy

ARE WARRANTSFOR OPERATIONSANALYSIS MET?

CONDUCTCOMPLETE TIA

STAFF REVIEW

SUGGESTED CHANGESREVISE REPORT

OK( STOP)

Figure 2 . 1 Flowchart Showing the Traffic Impact StudyProcedure


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CHAPTER III

PRELIMINARY STUDY

PRELIMINARY STUDY

A preliminary study will be required of all developmentsmeeting the preliminary warrants for traffic impact analysis.The preliminary study should include:

the type of development the complete site plan, with the site's access points

and the nearest signalized intersection in eachdirection

a market study (if applicable) trip generation, trip distribution and traffic as-

signment existing level-of-service of the adjacent roadway (s)

including the nearest intersections in each directionif they are within a reasonable distance of thesite (1/2 to 3/4 mile or one cycle length of traveltime, whichever is more)

.

horizon year level-of-service with and without pro-posed development

The preliminary study need not be a detailed analysis ofthe present and future conditions. No elaborate data collec-tion effort or computer modeling is necessary for such astudy. It is intended to provide an approximate analysis ofexisting and anticipated traffic conditions and is supposed toprovide some foundation on which to base the discussion during


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the initial meeting. The state department of transportation orthe local transportation agency may be contacted for anyexisting data that are available to conduct such an analy-sis.

The preliminary study should be submitted along with thepetition for an access permit.

PRELIMINARY WARRANTS

A preliminary study will be required of all developmentsmeeting the ^preliminary warrants'. The preliminary warrantsare based on certain predictor variables associated with theproposed development (at full "build-out") , such as grossfloor area, acreage, etc. Table 3.1 shows the quantitativethresholds of the predictor variables for different land uses.Developments having land use intensity greater than thethreshold values qualify for the preliminary study.

Table 3.1. Preliminary Warrants for Traffic Impact AnalysisLAND USE TYPE ITE CODE QUANTITATIVE THRESHOLDResidential

RetailOfficeIndustrialEducationalLodgingMedical

210, 220, 222,230, 270

814, 815, 820710, 714, 715,750,770110, 120, 130,140520, 530, 550310, 312, 320

610

150 Dwelling Units

15,000 square feet35,000 square feetor 3 acres70,000 square feetor 9 acres30,000 square feetor 250 students12 occupied rooms46,000 square feet


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10Special generators with high trip generation rates like

parking garages, banks (both drive-in and walk-in) , fast foodrestaurants, service stations with convenience stores, etc.will be required to submit a preliminary study, unless awaiver (for roads not under INDOT jurisdiction) is obtainedfrom the local public transportation agency (city, county,etc.) concerned. The reviewer (s) will decide whether or not awaiver is justified based on experience and engineeringjudgment.

For developments which cannot be grouped under one of theland use categories given in Table 3.1 or discussed in theprevious paragraph and for mixed-use developments, the tripgeneration rates should be determined using the latestavailable edition of the ITE Trip Generation report. If thedevelopment under consideration produces more than 50 peakhour peak direction vehicle trips, then the preliminarywarrants are satisfied. For developments that generate a lotof truck traffic, the truck trips should be converted toequivalent vehicle trips.

Developments that do not meet the preliminary warrantswill not be required to conduct any traffic impact analysis.

REPORT FORMAT

A sample report format for the preliminary study is shownin Appendix A.


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CHAPTER IV

WARRANTS FOR A COMPLETE TIA

A complete transportation impact study will be requestedfor any development that meets:

a) Warrant 1 and Warrant 2

b) Warrant 1 and Warrant 3

c) Warrant 4

Warrant 1. Land Use IntensityThis warrant is satisfied when a development generates

more than 100 peak hour peak direction trips.

Warrant 2. Level-Of-Service WarrantThis warrant is satisfied if the the traffic generated by

the proposed development causes the level-of-service of theadjacent streets/ intersections to drop by one letter grade.Level-of-service determination should be in accordance withthe procedures described in the Highway Capacity Manual [13].Warrant 3. Roadway Modifications

This warrant is met when the proposed development isexpected to significantly impact a roadway segment identifiedin the Transportation Improvement Program for improvement.This criterion is also met when the proposed developmentincludes modifications to the roadway system. Modificationsinclude addition of lanes to accommodate site-generated


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traffic, addition of exclusive turning lanes, accelera-tion/deceleration lanes, median openings, installation oftraffic signals and other traffic control devices, etc.

Warrant 4. Special CasesThis warrant is satisfied if the preliminary study

reveals that the traffic generated from the proposed devel-opment will create safety, operational or some other trafficproblems. Whether or not a development meets this warrantshould be decided at the initial meeting.


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CHAPTER V

TRAFFIC OPERATIONS ANALYSIS

Typically a traffic operations analysis is conductedwhenever a proposed development compromises the existingdesign standards and therefore might cause safety and opera-tional problems in the immediate vicinity of the site. Theanalysis should be done for the entire system and not just thedriveway or access point under consideration. A trafficoperations analysis might include:

1) Study of proposed driveway locations, resultingsight distances, gueueing provisions etc.

2) Safety analysis

3) Traffic signal warrants and progression analysis

4) Delay analysis

5) Gap studies

WARRANTS FOR TRAFFIC OPERATIONS ANALYSIS

A traffic operations analysis will be reguired if one ormore of the following conditions are satisfied:

1) A development generates more than 25 turning move-ments per hour.


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2) Request for new or modified driveways near intersec-tions, interchanges or on roads where the posted speedexceeds forty miles per hour.

3) Requests or probable need for a new (or modified)traffic signal to control driveways or streets servinga proposed or existing development (s)

.

4) Existing sight distance limitation or high accidentlocation near the site.

5) Requests for median openings on high speed facili-ties (posted speed limit >40 mph)


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CHAPTER VIINITIAL MEETING

The discussions in the initial meeting between the studypreparer/developer and the reviewer will be based on thefindings of the preliminary study. The meeting will serve thefollowing purposes:

1) To decide whether a detailed traffic impact study ortraffic operations analysis is reguired for the proposeddevelopment.

2) If further studies are reguired, the meeting will helpthe study preparer to assess the reviewer's expectations.

3) To discuss critical issues like extent of the study,study area, horizon years, time periods to be analyzed, datasources and availability, etc.

4) To ensure that all relevant issues are adequatelyaddressed in the traffic impact study.

If a traffic impact analysis is warranted, some of theissues that need to be addressed in this meeting are discussedbelow.


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STUDY AREA

Identification of an optimum study area is a prerequi-site to a proper TIA. An inappropriately large study area willunnecessarily increase cost and time. A small study area willfail to address the full impacts accurately. Any TIS shouldinclude at least all site access points and major intersec-tions adjacent to the site. The first signalized intersectionon each street serving the site should also be analyzed, if itis within 1/2 mile or one cycle length of travel time of thesite. Beyond this area, the review agency and the preparershould collectively determine any additional area to beanalyzed based on site specific issues. Sound engineeringjudgment should be used to include all areas that may directlyor indirectly be impacted by the proposed development.

HORIZON YEAR

The horizon year of a TIS should refer to the anticipatedcompletion date of the proposed development assuming fullbuild-out and occupancy.

TIME PERIODS TO BE ANALYZED

The critical time period for any development will bedirectly associated with the peaking characteristics of boththe development and the adjacent roadway system. These twopeak periods may overlap. In cases where they differ, the timeperiods that result in the two highest cumulative directionaltraffic demands should be used to assess the impact of sitetraffic on the adjacent roadway system and to define thechanges in roadway configuration and traffic control measuresneeded in the study area. In many cases, both the street andsite peaks have to be analyzed in addition to the two highestcumulative peak periods to ensure not only acceptable opera-


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tional levels on the roads but also provisions for drivewaycapacity, turn lane and queueing. Special consideration shouldbe given to developments like shopping centers, which mightpeak after the adjacent street peak or on a Saturday.

Unless decided otherwise, the following time periodsshould be considered:

i) AM and PM street peak (weekday)

ii) AM and PM site peak (weekday)

iii) Noon peak (weekday)

FUTURE OFF-SITE DEVELOPMENTS

Most studies will have to take into account future off-site developments to ascertain the "base condition" in thehorizon year. Off-site developments may be categorized undertwo broad headings:

Approved developments comprising the developments for whichzoning already exists and hence the land use intensity can beestimated.

Anticipated developments consisting of those that are expectedby the local agencies, based on the current comprehensive plananticipated in the horizon year. These may include land usesnot permissible under present zoning regulations.

The future off-site developments within the study areashould be realistic and consistent with recent developmenttrends. These should be available at a level of detail (byland use classification, intensity and location) appropriatefor the required transportation study.


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Both the reviewer and the study preparer should agree onoff-site development assumptions for the horizon year. In caseof a failure to reach an agreement, the reviewer will desig-nate the quantity, type and location and types of developmentsto be assumed in the study.DISCUSSION CHECKLIST

A discussion checklist has been provided in Appendix B toaid both the parties in recording information and comments.However, the discussions should not be restricted to theissues addressed in the checklist. The checklist has beendeveloped in line with the one used by the City of Indianapo-lis. Larger developments in densely developed areas will needmore in-depth discussion, while smaller sites might not needdiscussion on many of the issues in the checklist.

MEMORANDUM OF UNDERSTANDING

Immediately after the initial meeting, the study preparershould submit a memorandum of understanding confirming thefollowing [21]

issue to be addressed in the studystudy procedureassumptionsdata sourcesreport contentother pertinent issues discussed in the initialmeeting

The memorandum should request concurrence by the re-viewing agency staff.


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STAFF CONCURRENCE

The reviewing agency should review the contents of thememorandum. If they agree, they should communicate staffconcurrence to the preparer. This should be done in writing.

FIELD RECONNAISSANCE

The preparer should initiate the study by a preliminarysurvey of the study area and the proposed site to get a feelfor the site characteristics, traffic patterns, surroundingland uses, traffic control devices and geometric features ofthe site and surrounding roadways.

Table 6.1 gives typical data collection and fieldreconnaissance items.

Field reconnaissance should preferably be done before theinitial meeting, so that site-specific issues can be ade-quately addressed at the meeting.

REVIEWER RESPONSIBILITY

To ensure that all the relevant transportation issues areaddressed in the study, the reviewer should have a fairly goodidea about the type, location and intensity of the proposeddevelopment, adjacent roadway, peaking characteristics oftraffic in the study area, proposed and anticipated develop-ments in the study area, existing and anticipated zoning,available data sources, anticipated roadway and transportationsystem improvements in the horizon year and other relevantissues.


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Table 6.1. Typical Data Collection and Field ReconnaissanceItemsPeak Period (site and street) turning movement countsAdjustment factors to relate count data to designperiodMachine counts to verify peaking characteristicsPrimary traffic control devicesSignal phasing and timingRoadway configurationsGeometric features (curves, grades)Lane usageSight distanceParking regulationsStreet lightingDriveways serving site across from or adjacent to siteTransit stopsAdjacent land use

Source: Traffic Access and Impact Studies for SiteDevelopment, Proposed Recommended Practice, ITE, WashingtonD.C., 1991 (Final Report)

Table 6.2 lists typical data that might be needed for atraffic impact study.


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Table 6.2. Typical Background Data Needed for a CompleteTraffic Impact Study [Source: Ref.l]Category DataTraffic Volumes

Land Use

Demographics

TransportationSystem

OtherTransportation

Current and historic daily and hourlyvolume countsRecent intersection turning movementcountsSeasonal traffic variations, ifrelevantRelationship of count day to bothaverage and design days, if relevantProjected volumes from previousstudies or regional plansCurrent land use densities andoccupancy in the vicinity of the siteApproved projects, planned completiondates, densities and land use typesPrevailing development densities instudy areaAnticipated developments on otherundeveloped parcels, completiondates, etc.Comprehensive land use planZoning in vicinityCurrent and future population andemployment within study area by zoneCurrent street system characteristicsRoadwaysTruck routesRoute governmental jurisdictionTraffic signal locations, timings, co-ordinationAdopted regional planPlanned roadways and improvements inthe study areaTransit service and usagePedestrian and bicycle routesAvailable curb and off-site parkingObstacles to the implementation ofplanned projectsImplementation timing for study areatransportation improvements0-D data3 years accident history for accident-prone intersections


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CHAPTER VIIPREPARER AND REVIEWER QUALIFICATIONS

PREPARER QUALIFICATION

Traffic impact studies should be prepared by a trans-portation professional with training and experience in trafficengineering and transportation planning. It must be supervisedby a registered professional engineer with experience intraffic engineering operations.

REVIEWER QUALIFICATION

The traffic impact study shall be reviewed by one or moreof the professional staffs of the Department of Transportationand any other participating agency (Department of MetropolitanDevelopment, Department of Planning, City, County etc.) whocollectively have training and experience in traffic impactstudy methodology, land use planning and traffic engineering,including traffic safety and operations.

ETHICS AND OBJECTIVITYAlthough study preparers and reviewers might have dif-

ferent objectives and perspectives, they should adhere toestablished engineering ethics (similar to the Canon ofEngineering Ethics) and conduct all analyses and reviewsobjectively and professionally.


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CHAPTER VIIINON-SITE TRAFFIC ESTIMATE

For estimating the traffic impacts of a proposed devel-opment, it is essential to analyze the traffic conditions onthe horizon year roadway network for 2 cases: (a) with theproposed development and (b) without the proposed development.The incremental impacts are attributed to the site- generatedtraffic. For this, we have to establish the "base condition".The base condition will correspond to the traffic that wouldexist in the study area in the horizon year without theproposed development. This traffic is commonly referred to asnon-site traffic. Non-site traffic may be of two kinds [2]:

a) Through traffic, which has neither an origin nor adestination in the study area.

b) Traffic that has either origin or destination or bothin the study area. This traffic is generated by other develop-ments in the study area.

Non-site traffic estimation may be done by one of threemethods [ l ]

I. BUILD UP METHOD

The basic concept of this method is to estimate thetraffic generated by the proposed developments in the studyarea and to add it to the projected through traffic. If thesite under consideration is being redeveloped, the existing


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site traffic should be subtracted from the total to yield thefuture non-site traffic. The following steps should befollowed.

a) Identify Transportation System Improvements Trans-portation system improvements that are proposed, committed andprobable in the study area within the horizon year should beidentified. The resultant changes in modal splits and travelpatterns should be recognized.

b) Identify Study Area Developments All approved andprobable developments in the study area before the horizonyear should be identified by land use type, intensity andlocation.

c) Estimate Trip Generation The trip generation ratesof the land uses identified in step b should be estimated forthe horizon year using technigues consistent with Chapter 9 ofthis manual.

d) Estimate Directional Trip Distribution The direc-tional distribution of the estimated trips in step c should beascertained using methods consistent with Chapter 10 of thismanual.

e) Traffic Assignment The directional traffic in stepd has to be assigned to the horizon year roadway network usingmethods consistent with Chapter 11 of the manual.

f) Estimate Through Traffic Growth The existingthrough traffic has to be projected to the future year usingsome rate of growth decided by prior discussion with thereviewer.


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g) Obtain Future Traffic Add results of step e andstep f to get horizon year non-site traffic on different roadnetworks

.

h) Check Results Use engineering judgment to check thevalidity of the results obtained by the process and makeadjustments, if necessary.

This method is appropriate when considering a study areawith several major projects being developed during the sameperiod as the subject project.

II. USE OF AREA/SUB-AREA TRANSPORTATION PLAN OR MODELEDVOLUMES

Regional or sub-regional transportation plansgenerally project traffic volumes on major streets for about20 years into the future. Often interim projections are alsoavailable. Most of the projected volumes are in ADT thoughsome use peak hour volumes as well.

Projected traffic volumes from transportation planningstudies are particularly applicable to studies of very largeprojects with area-wide or regional impacts and in situationswhere the projections have local credibility and where networkdetails are consistent with that required for site trafficanalysis in the study area. This method would also be usefulfor large projects in highly congested corridors where majordiversion of through traffic might occur. The planning modelsallow reassignment of through traffic to alternate routesaround the areas with the added congestion of a proposeddevelopment. This method, however, should be used wherecredible demographic forecasts have been or can be quicklyprojected for the horizon year. Great care should be taken inconverting ADT to peak hour volumes.


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III. TRENDS OR GROWTH RATE METHOD

This method is based on the basic assumption thatrecent development trends and hence traffic volumes bothwithin and external to the study area will continue at thesame rate or change predictably. If recent growth rates arenot expected to continue, use of another method should beconsidered. Growth rates should not be normally applied incases where the horizon year is more than 10 years. This isbecause the growth rates cannot be expected to remain stablefor a greater period of time and the magnitude of error due toa relatively small error in the growth rate over a longerperiod of time.

Sometimes a combination of methods may be used to esti-mate future non-site traffic.


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CHAPTER IXTRIP GENERATION

Trip generation involves estimating the number of tripsthat will be produced from or attracted to the proposeddevelopment. This is one of the most important steps intraffic impact analysis.

ACCEPTABLE DATA SOURCES

Several sources and methods of obtaining trip generationdata are available and can be used:

I. ITE TRIP GENERATION REPORT ~ This report is intendedfor use in estimating the number of trips that may be generat-ed by a specific land use. The total data base is derived from1950 individual trip generation studies conducted over a spanof two decades. This report enables us to estimate tripgeneration based on three different options:

rateregression eguationsscatter plots

The estimates obtained from this source are however notto be used without sound judgment because they would corre-spond to the national average and would fail to take intoaccount any special features that the subject site might have.

II. OTHER NATIONAL DATA BASES Two other possiblesources for estimating trip generation are the NCHRP 187 [16]


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and Development And Application of Trip Generation Rates [4].The former contains trip generation rates for a variety ofland uses, mostly suburban. The latter is basically an updatedversion of NCHRP 187 with some statistical measures ofvariances of the data.

II. STATE AND LOCAL DATA Many states, regional andlocal agencies have trip generation rates for sites withintheir jurisdiction. Appropriate agencies can be contacted toexamine whether such data is available. The advantage ofworking with local data is that it will be more representativeof the site under consideration than national data.

IV. PRIOR STUDIES Data from prior studies made on asimilar kind of land use under similar conditions may also beused.

V. DATA COLLECTION If existing data are not availableor are not a good representation of specialized characteris-tics that the site under consideration might have, a datacollection effort has to be conducted at sites that exhibitsimilar characteristics as the study site.

RATES VS EQUATIONS

In cases where both rates and equations are available,sound judgment should be used to select the appropriate methodfor estimating the number of trips generated. Statisticalmeasures available, such as R-Squared values, standarddeviations, and visual evaluations should be made beforemaking a final decision. As a general rule of thumb, thefollowing procedure may be adopted to decide whether to userates or equations [27]:


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Step 1

.

Find out the trip generation rate using both theregression equation, (Trip) eqn , and the average rate,(Trip) rate . Calculate

{(Trip) eqn - (Trip) rate}/[{ (Trip) eqn + (Trip) rate }/2 ]

If the ratio is less than 0.05 then either of the two can beused. Ideally, the one that most closely represents the datapoints in the range of the independent variable should beused. If the ratio is greater than 0.05, then go to step 2.

Step 2

.

Use the regression equation if there are more than 20 well distributed data points

(for the independent variable under consideration) there are no predominant outliers the y-intercept is or nearly 0, and the R-squared value is reasonable.

Otherwise, go to step 3.

Step 3

.

Determine whether the regression line or the averagerate line more closely resembles the data points in the rangeof the independent variable. Use the one which more closelyresembles the data points. If neither of them fit well or bothfit equally well, go to step 4.

Step 4

.

Use regression equation if R2 > 0.75Use the rate if standard deviation < 110% of theaverage rate

If a decision still cannot be made, go to step 5.

Step 5. Use engineering judgment and find out which of the tworates found in step 1 (Tripeqn or Triprate ) more closelyresembles local trip generation characteristics. Refer toprevious studies or collect local data.


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AVERAGE VS EXTREME RATES

Most trip generation reports have an average rateaccompanied by the minimum and maximum rates. In such cases,the average rate should be used as a starting point with fullknowledge about the extremes. Thereafter, adjustments can bemade to the average rates using engineering judgment relatedto site-specific issues such as vehicle occupancy, transitusage, trip generation characteristics of the adjacent area,etc.

CHOOSING THE INDEPENDENT VARIABLE

When information is available for more than one inde-pendent variable, the predictive accuracy of the variablesshould be taken into consideration. In the planning stage, forexample, some variables are derived from others. Employmentand parking are generally estimated from the floor area.Therefore, floor area is the strongest predictor variable.Similarly, acreage is usually the weakest. If the tripgeneration rate of a development is known for more than onepredictor variables, statistical measures available like R-squared values, range, and standard deviation should be usedto determine the best independent variable. If the statisticalmeasures are more or less similar, the one with larger samplesize should be used.

DAILY AND SEASONAL VARIATIONS

Trip generation estimates for the average weekday isappropriate for most traffic impact studies. But in somespecialized cases, daily and seasonal variations might have tobe taken into account. Hotels, airports, and recreational landuses show seasonal variations. Similarly, shopping malls,restaurants and banks show daily variations. In such cases,


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the highest weekday rather than the average weekday tripgeneration rates should be used.

LOCATIONAL VARIATIONS

In making trip generation estimates, one should take intoaccount where the data was collected. Trip Generation andNCHRP data were, for example, collected mostly in suburbanlocations or outlying areas within central cities. Adjustmentsto these estimates might have to be made to consider site-specific issues. Also, issues like transit availability andusage, walk-in business, ride-sharing and other demandmanagement techniques should be given due consideration.

MIXED-USE DEVELOPMENTS

In case of mixed-use developments, certain deductionsmight have to be made to the trip generation rate derived byadding the trip generation rates of the individual land usesto accommodate the possibility of internal trips. Mixed-usedevelopments have been discussed in Chapter 13 of this manual.

PASS-BY TRIPS

The methodology of handling pass-by trips has beendiscussed in detail in Chapter 12 of this manual.


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CHAPTER X

TRIP DISTRIBUTION

After the trip generation estimates have been made, it isnecessary to distribute these trips to make an assessment ofthe impacts of the proposed development. The outcome of thetrip distribution method will be origin-destination data forgenerated trips.

DISTRIBUTION METHODS

Four methods of trip distribution may be used. Thesemethods are described below:

PRIMARY MARKET

The first step in this method is to identify the influ-ence area of the proposed development. This will correspond tothe area that contains 80 percent of the trip ends that willbe attracted to the site. The boundary of the study area maybe delineated by any of the methods described below:

a) If e market study is available, it should be used todetermine the influence area.

b) Delineate the influence area using a regular geometricshape, like a circle, with a radius corresponding to a traveltime appropriate for the type of development.


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c) Delineate the area by establishing the most distantpoints that can be reached within some selected travel timeover the existing street system.

d) Use Rilley's Law of Retail Gravitation to establishthe boundary between competing centers. This formulation ofthe gravity model considers the separation between the twocompeting locations as well as their relative sizes accordingto the following equation [2]:

dA = d^/ {l+(pB/pA ) 1/2 }dA = distance from center A to its primary market areaboundary with center BdAB = Distance from center A to center BPA = size of center APB = size of center B

Repeating the calculations from all competing develop-ments will yield certain points which, when connected, willgive the area of influence.

Once the area of influence has been identified, thefollowing procedure is to be adopted:

a) Divide the area into zones.

b) Determine the amount of activity in each zone.

c) Calculate the proportion of the activity in each zoneas a percentage of the primary market area.


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d) Identify the logical route from the centroid of eachzone to the site.

e) Calculate the directional distribution by assigningthe percentages to the minimum paths.

ANALOGY METHOD

This method involves identifying an existing site withsimilar or nearly similar characteristics as the subject site.Data for the existing site is collected or obtained fromprevious studies. Data collection effort may range from asimple driveway count including turning movements to anextensive license plate survey. The methods should be con-sistent with the Manual of Traffic Engineering Studies [25].

SURROGATE DATA

This method involves the use of what is popularly calledsurrogate data [1]. This method is useful if an extensive andusable socio-economic or demographic database exists by zoneor by sub-area. For example, population data can be used assurrogate data for retail trips. Employment is a reasonablesurrogate for residential trips. Other trips can also bedistributed using similar logical surrogates.TRIP DISTRIBUTION MODEL

Trip distribution using gravity models may be conductedmanually or by computer. In either case, the preparer mustdocument the procedure properly. Local Metropolitan PlanningOrganizations have data by zones that might be used. Theprocedure, both manual and computerized, produces direction of


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approach information and reduction in site traffic at anincreased distance from the site. Hence the gravity modelapproach is useful when it is necessary to evaluate thetraffic impacts of developments on intersections at certaindistance from the site. This method, however, should be usedfor large projects, because for small distances from the site,the estimates are too rough.


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CHAPTER XI

TRAFFIC ASSIGNMENT

Traffic assignment involves assigning the distributedtrips to specific paths in the road network. Hence, theproduct of traffic assignment will be the total project-generated traffic by direction and by turning movements on thehorizon year roadway network in the study area. Assignmentshould be made after taking into account logical routing,available roadway capacities and projected and perceivedminimum travel times. Multiple paths should be assignedbetween origins and destination rather than assigning all ofthe traffic to the route with the shortest travel time.

The assignment may be done manually or by computer.

Procedures for assigning site and non-site trips are thesame.


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CHAPTER XII

PASS-BY TRIP

Shopping centers and several other convenience-orientedland use types like banks, gas stations and fast food res-taurants have different trip characteristics than other landuse developments. A significant portion of their trips are"captured" from the adjacent traffic stream. These tripsalready existed before the development. Trips to such devel-opments may be broken down into 3 categories [5,9,10]:

Primary Diverted Pass-by

Figure 12.1 shows primary, pass-by and diverted linkedtrips.

A primary trip destined to a retail facility is one inwhich the purpose of the trip is shopping at the site and thepattern of the trip is home-shopping-home.

A diverted linked trip to a retail facility is one inwhich the shopping destination is a secondary part of theprimary trip, such as work to shopping to home. Thus thediverted linked trip involves a route diversion from theroadways adjacent to the site to reach a retail facility.

The pass-by trip comes directly from the traffic streampassing the facility on the adjacent roadway system and doesnot require a diversion from another roadway.


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PASS-BY TRIP

ARY TRIP

Figure 12.1. Schematic Diagram Showing Primary, Pass-by andDiverted Linked Trips

The percentage of pass-by trips vary with the size andtype of development, its geographical location, time of theday, and the nature of the roadway system.

It is evident that all trips are not new to the area anda reduction in the effective trip generation rate is justi-fied. However, it is incorrect to simply reduce the tripgeneration rate by the estimated pass-by percentage. Thiswould fail to take into account the actual distribution oftraffic around the site, which can have a significant impacton the outcome of the analysis. The pass-by trips can signifi-


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cantly impact the turning movements once the site becomesoperational.

METHODOLOGY

The methodology for handling pass-by trips during atraffic impact analysis is discussed below [7].

1) Estimate the trip generation rate as described inChapter 5

.

2) Estimate the percentage of pass-by trips. This may bedone by either collecting data, using surrogate data, or usingITE Trip Generation data. Whatever the method chosen, engi-neering judgment should be used and there should be concur-rence between the preparer and the reviewer on this matter.

3) Split the total trips generated into two separatecomponents:

i) pass-by tripsii) new trips

New trips include the primary and the diverted linkedtrips.

4) Estimate trip distribution for the two individualcomponents separately.

5) Conduct two different traffic assignments one forpass-by and one for new trips. Assignments should takeinto account the capacity constraints and travel timeson different links. The distribution and assignment of


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pass-by trips will result in percentages being sub-tracted from some intersection approaches and beingadded back to another.

6) Combine the two assignments to get the final linkloadings.


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CHAPTER XIII

MIXED-USE DEVELOPMENTS

Mixed-use developments refer to activity centers thathave a number of different land uses. In such cases it isoften inappropriate to simply add up the trip generation ratesof the individual land uses to determine the trip generationrate of the entire development. This is because some individu-als will visit two or more destinations without leaving thesite. Therefore, to estimate the trip generation rates of suchdevelopments, the number of internal trips have to be estimat-ed and subtracted according to the following formula:Trips generated = (trips generated by - internal tripsfrom mixed-use individual land uses)development

In the absence of local or site-specific data, thepercentages given in NCHRP Report 323 [15] and ITE TripGeneration [5] can be used as a guideline for determining thepercentage of internal trips.


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CHAPTER XIVANALYSIS

Several analyses are necessary to derive the studyfindings, recommendations and conclusions. The differentanalysis that might be required are:

Capacity AnalysisSafetySite Access PointsTraffic Control NeedsMedian OpeningsOn-site Circulation and ParkingNeighborhood impacts

For each horizon year, the analysis should be performedfor the critical time period for conditions with and withoutthe proposed development. The incremental impacts can beattributed to the subject site.

The analysis should not be ended until one of threeconclusions has been reached:

1) The proposed development can be accommodated in thehorizon year transportation infrastructure with no additionalimprovements

.

2) The proposed development can be accommodated in thehorizon year transportation infrastructure consistent with


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agency policy and operating conditions subject to the recom-mended improvements/modifications

.

3) The area will operate below the accepted level ofservice even without the development. No further significantdeterioration will result if the proposed development isaccommodated with the recommended changes.

CAPACITY ANALYSIS

Capacity analysis should be performed at all proposedsite access points and all intersections both signalizedand unsignalized in the study area. Other critical andcongested areas of the roadway network should also be identi-fied for analysis by the reviewing agency. Elements such asfreeway weaving sections, ramps, etc. might also reguirecapacity analysis.

Capacity analysis should be consistent with the methodsdescribed in the 1985 edition of the Highway Capacity Manual(HCM) [13]. The latest available FHWA version of the HighwayCapacity Software should be used for capacity analysis.

Signalized Intersection LOS DeterminationChapter 9 of the Highway Capacity Manual suggests two

methods for LOS determination for signalized intersection:planning and operational. For studies with a horizon year ofless than 10 years, an operational analysis should be con-ducted. For a horizon year of greater than 10 years, either ofthe two methods can be used.

Unsignalized Intersection LOS DeterminationUnsignalized intersection LOS is based on reserve

capacity. The Highway Capacity Manual LOS procedure (Chapter10) computes capacity for each movement based upon the


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critical time gap required to complete the maneuver and thevolume of traffic that is opposing the movement.

A gap analysis may provide assessment of whetherseparate turn lanes are needed. Combined with a signalwarrant study, this analysis will also aid in the determina-tion whether signalization should be considered.

Urban and Suburban ArterialFor developments along existing arterial roadways, it is

necessary to assess the impact of the new traffic on theoperation of the through street. Chapter 11 of the HCMdescribes arterial roadway capacity based on operating speedand type of facility. In the simplest case, the requiredanalysis may consist of a time-space diagram to show that aproposed signal will, or will not, affect the platoon flowoperating on the arterial. For complex cases, computerpackages like the AAP, PASSER and NETSIM may be used. Thestudy procedure and results must be documented in all thecases.Freeway Capacity Analysis

Freeway interchange areas serving major developments haveto be evaluated in terms of ramp capacities, ramp design andconfiguration, and weaving section capacities, as per theHighway Capacity Manual (Chapters 3 through 6) . Queue storagerequirements can also be developed using queueing analysis.

SAFETY ANALYSIS

Safety analysis should include identification and recom-mendations about high accident locations, sight distanceanalysis and pedestrian safety. These are discussed brieflybelow.


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Accident ExperienceThe review of the existing data for the study area should

include recent accident records. Locations where trafficsafety should be given additional consideration should beidentified. Possible methods to alleviate the existing hazardsshould be analyzed.

Locations having accident rates higher than one accidentper million entering vehicles should be given special con-sideration [21].

Sight DistanceAn analysis of site distances should be made to ensure

that there is adequate unobstructed sight distance in bothdirections on all approaches to an intersection. The sighttriangle for all unsignalized intersections should be deter-mined using the space-time-velocity relationship described inA Policy on Geometric Design of Highways fAASHTO) . In asignalized intersection, however, the unobstructed sightdistance may be limited to the area of control [14].Pedestrians and Bicycles

The site plan should be reviewed to ensure that theinternal circulation pattern and external access points aredesigned for pedestrian safety and to minimize pedestri-an/vehicle conflicts. Locations for transit stops and theassociated pedestrian flow to and from parking facilities needcareful consideration during site planning.

In case of heavy pedestrian traffic, pedestrian LOSshould be determined using HCM (Chapter 13)

.

Due consideration should be given to bicyclists' safetyand circulation.


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SITE ACCESS POINTS

The site access points provide the link between theadjacent roadway system and the proposed development. Drive-ways provide intersections with public streets. To satisfac-torily provide site access and maintain acceptable operationalconditions on the adjacent streets, the agency's accesscontrol policy and standard principles must be followed. Incase of multiple driveways, transportation-related needs formore than one driveway must be demonstrated.

Both street peak and site peak should be taken intoconsideration while analyzing the site access points.

All site access points should conform to the IndianaDriveway Handbook .

Provision should be made for vehicular storage. A 95%probability of storing all vehicles should be assumed.

TRAFFIC CONTROL NEEDS

Analysis should be carried out to determine whethertraffic control warrants are met. Such warrants may bewarrants for traffic signals, stop and yield signs. Thewarrant analysis should be according to the Indiana Manual ofUniform Traffic Control Devices [23].

MEDIAN OPENINGS

If a median opening is requested, a detailed analysisshould be carried out to find out whether a median openingwould hamper the operating condition of the roadway. Dueconsideration should be given to the following: warrants for a left turn signal at the opening [20]


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approach speed of the opposing vehicles gaps in opposing traffic storage space at the median opening queueing and delay to the vehicles distance from nearest intersection spacing between median openings [2,31]

ON-SITE REVIEW

In most cases, on-site review will not be included in atransportation impact study. For very large projects, whereinternal circulation system is critical, on-site review may benecessary. On-site review should include review of internalcirculation and parking.

ParkingProviding adequate parking facilities for any development

is of utmost importance in site planning. Insufficient parkingleads to inconvenience, damage to parked vehicles, illegalparking, reduction in capacity and sight distance and conse-quently, congestion and accidents respectively. ITE ParkingGeneration [26] can be used to estimate parking demands.

Parking should be according to the existing zoning ordi-nance. Any variance should be requested and well documented.In case of shared parking between mixed-use developments,guidelines provided in Shared Parking [29] should be followed.

Internal CirculationInternal circulation should provide access to all areas

in a manner easily understandable to the drivers. Internalroadways should be marked and signed in accordance withrecommendations in the Indiana Manual of Uniform TrafficControl Devices [23].


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Consideration should be given to service and deliveryvehicles and emergency vehicles in site design.

NEIGHBORHOOD IMPACTS

Neighborhood transportation impacts are primarily causedby site-generated traffic using neighborhood streets as shortcuts. This can hamper pedestrian safety, air quality, communi-ty cohesion and, consequently, property values. Most neighbor-hoods are sensitive to this and hence an analysis should beconducted to estimate the neighborhood impacts of the proposeddevelopment and mitigating measures suggested.


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CHAPTER XVCONCLUSIONS AMD RECOMMENDATIONS

If the analysis reveals that the projected trafficvolumes on the horizon year roadway network will operate in asafe and efficient manner at an acceptable level of service,then no improvements are required. However if deficiencies aredetected, mitigating measures have to be recommended.

These may include :

1) Installation of traffic signals

2) Installation of traffic control signs

3) Addition of lanes

4) Addition of acceleration and deceleration lanes

5) Restricted turn movements

6) Adjusting cycle lengths

7) Introducing additional signal phases

However, if reasonable mitigating measures cannot befound to make the traffic operate in an efficient way, a moredetailed analysis of project size, land use and developmentphasing may be required. If viable transportation improvementscannot be recommended, then steps have to be taken to reduce


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the trip generation rate of the proposed development duringthe problem period. Some of the possible approaches that maybe adopted, include:

increased transit usage carpool/vanpool congestion pricing reduced parking staggered work schedules

Several transportation demand management technigues thatcan reduce peak hour traffic are listed in Table 15.1.

Any of these methods finally accepted have to come witha written commitment from the petitioner to implement thenecessary programs to ensure that the expected reductionoccurs.

The recommendations should take into account [22]:

1) Timing of the short and long-range transportationsystem improvements that are already scheduled or

anticipated.

2) Anticipated timings of adjacent developments.

3) Development phasings of the subject development.

4) ROW needs and availability.

5) Local priorities of transportation improvementfunding.

6) Cost-effectiveness of the proposed improvements.


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Table 15.1. Transportation Demand Management Techniques WithPotential to Reduce Site Traffic Generation

LIKELY VEHICLE TRIP REDUCTIONS

MEASURES OFFICE RETAIL INDUSTRIAL RESIDENTIAL LODGING EVENT CENTERS

Substantial transit service toareas of trip origin T,P T,PH T,P T,P T,P r,P

Carpool/vanpool T,P t,ph T,P - r,p T,P

Modified work schedules P - P P - -

Parking availability reducedbelow norial deiand level or T,P 1 T,P T,P T,P T,Pincreased parking cost

Internal shuttle transportationwhen site is part of lajor T,r1 T,H - T.H T,P -developient well served by shuttle

Transit subsidy T,P - T,P T,P 7 >

Quality pedestrian enviromenton-site (med-use developients) T,H T,N T,H T,P,1 T.P.H T.P.H

T = daily trips, P = peak hour trips, PMtrips, M = midday trips p.m. peak hour


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RECOMMENDED PLAN OF ACTION

Implementation recommendations should be presented as a"plan of action". This action plan should recommend improve-ments, state why they are needed, and when they are to beimplemented.


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CHAPTER XVI

REPORT

The traffic impact study report should document thepurpose, procedures, data sources, assumptions, findings,conclusions and recommendations of the study.

Reports should be concise and complete. It should beorganized in a logical sequence and methodically take thereader through the entire process of traffic impact analysis.It should be kept in mind that the report might be of interestto the decision makers and other non-technical people. Hence,clarity should not be sacrificed.

REPORT FORMATReport Cover and Title Page

See Appendix C

Table of ContentsEach report should have a table of contents listing all

the chapters and major sections.

List of ExhibitsA list of exhibits should be provided, which should list

all the tables and figures included in the report by page num-ber.

Some of the typical exhibits that should be included ina traffic impact study are tabulated in Table 16.1.


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Executive SummaryEach traffic impact study report should begin with an

executive summary. It should be one-page or two-page documentto facilitate examination by the reviewing agency. It shouldcontain the salient features of the study and should summarizethe study purpose, and its conclusions and recommendations.Letters and memorandum reports under 10 pages do not need anexecutive summary.

Prototype Report OutlineA prototype report outline is given Appendix C.

Report CertificationThe DOT may wish to require that traffic impact studies becertified by the preparer. Such certification should statethat the study has been conducted according to the methoddescribed in the manual.

A report for any of the limited studies or trafficoperational analyses should state in the first paragraph thatthe reviewer directed or agreed that only a limited study beconducted.

PUBLIC RECORD

Traffic impact study reports become public record uponsubmittal. Information provided in the study can be used forsubsequent studies.


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Table 16.1 Typical Exhibits in a Detailed Traffic Impact Study[Source: Reference 1]

ITEM TITLE DESCRIPTION

Figure A

Figure B

Figure C

Figure D

Figure E

Figure F

Table A or,Figure G

Table B

Figure H

Table C

Figure I

Figure J

Figure K or,Table D

Figure L or,Table E

Site location

Existing transportationsystem

Existing and anticipateddevelopment

Current traffic voluies

Existing peak hour turning

Anticipated transportation

Directional distribution

Estimated site trafficgeneration

Site traffic

Trip generation ofnon-site development

Estimated non-site traffic

Estimated total horizon yeartraffic

Level of Service

Recommended Improvements

Area map showing site location and area ofInfluence.

Existing roadway system serving site. Should shotall major & minor routes adjacent to the site.

Hap showing existing and anticipated land uses/developments In study area

Most recent traffic volumes on roads In the studyarea

Current peak hour turning volumes at each locationcritical to the study

Area transportation system map showing programmedand applicable planned roadways, improvementsIncluding transit, blkeways and pedestrlan-waysImprovements affecting site access or traffic flowthrough the study area.

Map or table showing the proportion of site trafficapproaching and departing the area on each roadway

Analysis period site traffic generation by direction

Map of horizon year roadway network showing peakhour turning volumes of site generated traffic

Trips generated by off-site developments withinwithin study area.

Map showing peak hour turning volumes doe toother developments In study area and through traffic

Peak hoar turning movements In horizon year.(Sum of figures B 4 I)

Level of service at critical locations under presentconditions and In horizon year with & without theproposed development.

Table or figure showing Improvements by location 1type. If phasings of Improvements are to bestipulated they have be shown.


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CHAPTER XVII

STAFF REVIEW

The purpose of staff review is to ensure that the trafficimpact study (TIS) is proceeding in the right direction andthat the recommendations made by the preparer are realisticand implementable. Staff reviews are not intended to deter newdevelopments. They are to ensure that traffic- relatedproblems are foreseen and effective mitigation measures areidentified.

Traffic impact studies should be reviewed by departmentsand agencies that are (a) responsible for operating theroadways, and/or (b) planning and implementing roadwayimprovements that are likely to be impacted by the proposeddevelopment.

FORMAL REVIEW

This review is conducted after the report has beensubmitted by the preparer. The formal review process shoulddevelop a list of the following findings:

Acceptable analyses and conclusionsUnacceptable analyses and conclusionsAcceptability of recommended site access provisionsand roadway improvementsList of required improvements that might be consideredto mitigate impacts of the proposed development.


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Following the review, the reviewer (s) should send tothe preparer a list of requested study revisions or a letteraccepting the study.

REQUEST FOR REVISIONAny requests for study revisions should concisely

indicate the findings of the formal review and clearly specifythe additional information required. This additional reportshould be in the form of an addendum to the original study. Incertain specific cases a revised report may berequested.


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BIBLIOGRAPHY

1. ITE, A Recommended Practice - Traffic Access and ImpactStudies for Site Development (Final Report) , 1991,Washington D.C.2. Stover, V.G., and Koepke, F. J. , Transportation and LandDevelopment . 1988, Prentice Hall.3. Keller, R.C. and Mehra, J., Site Impact Traffic Evalua-tion (S.I.T.E.) Handbook, Report # FHWA/PL/85/004

,

January 1985, FHWA.4. Keller, R.C, and Mehra, J., Development and Applicationof Trip Generation Rates, Report # FHWA/PL/003 , January1985, FHWA.5. ITE, Trip Generation . 5th Edition, 1991, Washington D.C.6. Bonneson, J. A., "Traffic Volume Adjustments for ImpactAnalysis", ITE Journal , April 1987, pp. 43-46.7. Smith, S.A., " A Methodology for Consideration of Pass-By Trips in Traffic Impact Analyses", ITE Journal .August 1986, pp. 37-39.8. Colorado/Wyoming Section Technical Committee - TripGeneration, "Trip Generation for Mixed-Use Develop-ments", ITE Journal . February 1987, pp. 27-32.9. Kittelson, W.K. and Lawton, T.K. , "Evaluation ofShopping Center Trip Types", ITE Journal . February 1987,

pp. 43-51.10. Toth, Z.B., Atkins, D.M. , Bolger, D. and Foster, R.

,

" Regional Shopping Center Linked Trip Distribution",ITE Journal . May 1990, pp. 41-46.11. Scully, W.J., Rydant, R.A. and Brenner, K.J.,"Developing Forecasting Data for Factory OutletCenters", ITE Journal . February 1991, pp. 41-47.


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12. Moussavi, M. , and Gorman, M. , "A Study of Pass-By TripsAssociated with Retail Developments", ITE Journal . March1991, pp. 43-47.13. TRB, Highway Capacity Manual . Special Report 209, 1985.14. AASHTO, A Policy on Geometric Design of Highways . 1984,pp. 774-796.15. Hooper, K.G., Travel Characteristics at Large-scaleSuburban Activity Centers, NCHRP Report 32 3 . October1989, Washington D.C.16. Sosslau, A.B., Hassam, A.B., Carter, M.M. and Wickstrom,G.V., Quick-Response Urban Travel Estimation Techniquesand Transferable Parameters, NCHRP Report 187 . 1978,Washington, D.C.17. FHWA, Site: Methodology and Micro-Computer Methods -Student Workbook, FHWA-HI-88-046, November, 1987.18. Luh, J.Z., and Lothian, W.G., "Traffic ProgressionAssessment in Traffic Impact Analysis", ITE Journal , May1991, pp. 17-21.19. ITE, Transportation and Traffic Engineering Handbook ,Washington, D.C.20. Kell, J.H. and Fullerton, I.J. , Manual of Traffic SignalDesign . 1982, Prentice Hall, Inc.21. Barton-Aschman Associates, Inc. , Procedure Manual -Transportation Impact Studies for Proposed Development,City of Indianapolis, October 1990.22. Barton-Aschman Associates, Inc., Applicant's Guide -Transportation Impact Studies for Proposed Development,City of Indianapolis, October 1990.23. Indiana Department of Highways,, Indiana Manual of

Uniform Traffic Control Devices for Streets andHighways, 1981.24. Meyer, M.D. and Miller, E.J., Urban TransportationPlanning A Decision Oriented Approach . McGraw Hill,Inc., 1984.25. Box, P.C. and Oppenlander, J.C., Manual of TrafficEngineering Studies . Fourth Edition, ITE, Washington,D.C. ,1987.26. ITE, Parking Generation . Washington, D.C, 1987.


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27. ITE Technical Council Committee 6A-32, "Guidelines forUsing Trip Generation Rates or Equations", ITE Journal .August 1990, pp. 14-16.28. Bochner, B., Hooper, K. and Rifkin, A., "Traffic Accessand Impact Study for Site Development An ITE

Educational Foundation Seminar, ITE, March 1990.29. Urban Land Institute, Shared Parking . Washington, D.C.,1983.3 . Homburger , W . S . , Transportation and Traffic EngineeringHandbook . Washington, D.C., 1982.31. FHWA, Access Management, Location and Design, FHWA-HI-92-

033, October 1991, FHWA


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APPENDIX ASAMPLE PRELIMINARY STUDY OUTLINE

Report Cover

A. Development NameB. Application NumberC. Applicant NameD. Preparer Name and OrganizationE. Report Date

Title Sheet

A. Development Name and LocationB. Application NumberC. Applicant's Name, Number and Telephone NumberD. Preparer's Name, Title, Organization, Address and

Telephone NumberE. Date of Original Report

Table of Contents

List of Figures and Tables

I. Introduction

A. Purpose of Report and Study Objective


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II. Proposed Development

A. Land use and IntensityB. Area Map Showing Site LocationC. Site PlanD. Location of nearest signalized intersection in

each direction

III. Market Analysis (if applicable)

IV. Figure showing present traffic volumes at intersectionsto be analyzed

V. Trip Generation

VI. Trip Distribution

VII. Traffic Assignment

VIII. Figures showing horizon year traffic volumes atintersections to be analyzed with and without theproposed development

IX. Table summarizing the results of the capacity analysesfor the three conditions: (a) present condition,(b) future condition without development, and (c) futurecondition with development

X. Summary and Conclusions


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APPENDII BINITIAL MEETING CHECKLIST

Date:Time:Place:

People AttendingName, Organization and Telephone #:1)2)3)4)5)

Study PreparerPreparer's Name & Title:Organization:Address & Telephone #:

Reviewer (s)Reviewer's Name & Title:Organization & telephone #:

Reviewers 's Name & Title:Organization & Telephone #:

ApplicantApplicant's Name, Address & Telephone #:


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Proposed DevelopmentName:Location:Location Within Area:1) CBD 5) Rural2) Urban (Non-CBD) 6) Freeway Interchange3) Suburban (Non-CBD) 7) Other (Specify)4) Suburban CBDLand Use Type :

ITE Code #Other :Description

Proposed # of development units:

ZoningExisting:Comprehensive Plan RecommendationRequested

Findings of the Preliminary Study:

Study Type:Complete Traffic OperationsNone


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Study AreaBoundaries:

Additional Intersections to be analyzed:

Horizon Year(s)

Analysis Time Period fs)

Future Off-Site Developments

Source of trip generation rates

Reductions in trip generation ratesNonePass-by tripsInternal trips (mixed-use developments)Transit UseOther

Horizon year roadway network improvements


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Methodology & AssumptionsNon-site traffic estimates:

Site-trip generation:Trip distribution method:

Traffic assignment method:

Traffic Growth rate:

Special Features (from preliminary study or priorexperience)

Accident locations:

Sight Distance:

Queueing:

Access Location & Configuration:

Traffic Control:

Signal System Location & Progression Needs:

On-site parking needs:


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Data Sources:

Base Maps:Prior study reports:

Access policy and jurisdiction:

Review Process:

Requirements

Miscellaneous

SIGNATURES

STUDY PREPARER REVIEWERS APPLICANT


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APPENDIX C

SAMPLE REPORT OUTLINE

Report Outline

A. Development Name and LocationB. Application NumberC. Applicant NameD. Preparer Name and OrganizationE. Report Date

Title Sheet

A. Development Name and LocationB. Application NumberC. Applicant's Name, Address and Telephone NumberD. Preparer's Name, Title, Organization, Address

and Telephone NumberE. Date of Original ReportF. Report Revision Date

Table of Contents

List of Figures and Tables

I. Introduction and Summary

A. Purpose of Report and Study ObjectivesB. Executive Summary

1. Site location and study area


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2. Development description3. Principal findings4. Conclusions and recommendations

II. Proposed Development

A. Subject Site1. Land use and intensity2

.

Location3. Site plan4. Zoning4. Phasing and timing

B. Off-site Developments

III. Area Conditions

A. Study Area LimitsB. Study Area Land Use

1. Existing land use2. Existing zoning3. Anticipated future developments

C. Site Accessibility1. Area roadway system

a. existingb. proposed

2. Traffic volumes3

.

Transit service4

.

Transportation system management programs

IV. Projected Traffic

A. Site Traffic ( each horizon year )1. Trip generation2. Trip distribution


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3. Traffic assignment

B. Non-Site Traffic ( each horizon year )1. Method of projection2

.

Trip generation3

.

Trip distribution4. Traffic Assignment

C. Total Traffic ( each horizon year )V. Analysis

A. Site AccessB. Capacity and Level of ServiceC. Traffic SafetyD. Traffic ControlE. Site Circulation and Parking

VI. Improvement Analysis

A. Improvements to Accommodate Non-Site Traffic1. Physical2. Operational

B. Additional Improvements to Accommodate SiteTraffic

1. Physical2

.

Operational3

.

Travel demand reductionC. Alternative ImprovementsD. Status of Improvements Already Funded,

Programmed or PlannedE. Evaluation


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VII. Findings

A. Site AccessibilityB. Traffic ImpactsC. Additional ImprovementD. Compliance With Traffic Related Local Codes

VIII. Recommendations

A. Site Access/Circulation PlanB

.

Roadway Improvements1. On-site2. Off-site

C. Transportation System Management ActionsD. Other

IX. Conclusion

A. Traffic Impact of Proposed DevelopmentB. Adequacy of Proposed Plan Including Recommended

Improvements


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manual of traffic i 00 dey s

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