26 TR News, March–April 1987

RESEARCH PAYS OFF

The Highway Capacity ManualDevelopment and Application

Problem

The major problems facing motorists ontoday's highways are congestion, acci-dents, and costs—too many automo-biles traveling to the same place at thesame time; too many automobiles,trucks, buses, bicycles, and pedestriansattempting to use the same space; toomany motorists losing time unneces-sarily; too many accidents occurring;and too many decisions being made onhighway improvements without ade-quate analytical tools.

From these problems comes the needto quantify congestion and highwayoperations in such a way that rationalsolutions can be determined. For morethan 35 years, the Highway CapacityManual has been used extensively forthis purpose. However, much haschanged in the years since the earliereditions were published, regarding bothtravel characteristics and improved pro-cedures for capacity analyses. Travelcharacteristics have changed because ofa shifting mix in both the driver andvehicle populations, and also becauseoperational changes have occurred,such as the 55-mph speed limit and theright-turn-on-red regulations. Researchby many individuals, private organiza-tions, and public agencies has led tonew understandings and insights,which, in turn, have resulted in proce-dural revisions and new techniques in

highway capacity analysis. The com-bined effect of these changes created apressing need for a revised manual.

Solution

In the early 1970s the National Coop-erative Highway Research Program(NCHRP) and the Federal HighwayAdministration (FHWA) initiated ma-jor research efforts to study variousaspects of highway capacity analysis.Final preparation of the 1985 HighwayCapacity Manual was accomplishedby the Transportation Training andResearch Center of the PolytechnicInstitute of New York with the assis-tance of the Texas Transportation In-stitute of Texas A&M University. Theresearch team performed massive ed-iting of source materials in order toprovide a uniform approach, philoso-phy, and style. Some procedures un-derwent additional development, whileothers were only slightly modified. Allof this work was done under the guid-ance of the Transportation ResearchBoard Committee on Highway Capac-ity and Quality of Service.

More than 60 professionals directlyparticipated in substantive reviews ofthe procedures through the TRB com-mittee and its several subcommittees.More than 30 NCHRP panel and TRBcommittee meetings were held during

the 8 years of development. Each of the14 chapters of the 500-page manualwent through at least three drafts andcycles of review and revision, and wassubmitted to at least 32—and as manyas 200—reviewers. More than 750pages of reviewers' comments werereceived. This effort culminated in thepublication of the third edition of theHighway Capacity Manual by TRB inAugust 1985.

Application

The 1985 Highway Capacity Manual. acollection of procedures and method-ologies for calculating highway capac-ity and level of service, neither consti-tutes nor attempts to establish legalstandards for highway construction. Itprovides methods for analyzing in ad-vance the quantity of service a highwaycan provide as well as the quality ofthat service. In particular, the 1985manual will change the way analystsconsider service quality and will pro-vide greater flexibility in adapting pro-cedures to actual conditions. Designedfor use in planning, design, and opera-tional analyses, the manual is particu-larly relevant to the current concerns ofmaximizing the utility of existingstreets and highways.

Unlike previous editions, the High-

TR News, March–April 1987 27

way Capacity Manual will be updatedcontinuously on a chapter-by-chapterbasis, so that users may benefit fromthe latest research as soon as it is prac-ticable. To permit this continual updat-ing, the 1985 manual was published inloose-leaf form.

Because of the complexity of some ofthe new analysis methods, there was aneed for microcomputer software. TheFHWA responded by developing mi-crocomputer software to provide anofficial set of programs and greateruniformity in their application. TheFHWA is also developing a set oftraining materials for use in shortcourses. Many universities have beenusing the new Highway Capacity Man-ual since September 1985 in both shortcourses and undergraduate and graduatecurricula.

Benefits

The 1985 Highway Capacity Manualrepresents the latest approach to makingmajor decisions about highway con-struction and operational improve-ments. Quantifying the benefits of abetter approach is practically impossi-ble; however, even without looking atnumbers, it is clear that, with the mostconservative estimates of savings, animpressive benefit-cost ratio exists forthe research that led to the new manual.

Even less quantifiable but equallyimportant are benefits in the form ofconsistency, reliability, and recognizedcredibility. With nearly 20,000 copiesof the publication already in use, deci-sions will not only be better, they willbe more consistent from project to proj-ect, from city to city, and even among

different countries. Furthermore, peoplewith limited technical training will bebetter able to conduct technical analy-ses, and will be able to do so even moreeasily with introduction of the newsoftware. Finally, in an age in which theavailability of a recognized set ofcredible procedures is a requirement inconvincing the courts that acceptabletechniques are being used, the manualhas proved to be a valuable tool withsignificant benefits to the highway pro-fession.

To obtain a copy of the 1985 HighwayCapacity Manual, published as TRB SpecialReport 209, contact the Business Office,Transportation Research Board, 2101 Con-stitution Avenue, N.W., Washington, D.C.20418 (telephone: 202-334-3218) (price:$40.00). The FHWA computer programscan be ordered from the McTrans Center,512 Weil Hall, University of Florida,Gainesville, Fla. 32611 (telephone: 940-392-0378) (price: $50.00). Information onthe FHWA training courses can be obtainedfrom Dennis Lee, FHWA, HTO-31, 7th andD Streets, S.W., Washington, D.C. 20590(telephone: 202-366-1993).

Suggestions for "Research Pays Off" ar-ticles are welcome. Contact Nancy A.Ackerman, Editor, TR News, Transpor-tation Research Board, 2101 Constitu-tion Avenue, N.W., Washington, D.C.20418 (telephone 202-334-2972).