The Highway Capacity Manual
(HCM) is the most widely used resource for traffic analysis. Software makes the HCM relatively easy to use, but many users lack a thorough understanding of the HCM methodologies. Inappropriate use of this tool can lead to highways that have insufficient capacity, increasing pollution and congestion, or that are overbuilt and wasteful of public funds.
The 1994 HCM only provided simple example problems to illustrate the methodologies. Complex, real-world problems require more than plugging numbers into formulas. Realistic applications would educate users on how to properly use the HCM for these types of problems. These applications also can help identify limitations in the methodologies, including when their use is inappropriate, and they could be used as resources in training classes and self study.
The objective of this research was to develop a Highway Capacity Manual (HCM) Applications Guide that shows how to appropriately apply HCM 2000 methodologies to real-world problems and indicates when other methods may be more appropriate. The guide uses sample applications to illustrate how the user should develop input data sets, select an appropriate analysis method, identify limitations in the HCM methods, and interpret the analysis results.
The HCM Applications Guide (which is based on the HCM 2000) is available at https://hcmguide.com
. NCHRP Research Results Digest 287
summarizes the contents of the Highway Capacity Manual Applications Guide. The HCM Applications Guide was incorporated into Volume 4 of the HCM 2010.
Accomplishment of the project objective will require the following tasks: (1) Develop a categorized inventory of real-world analyses in which HCM methodologies are commonly used (e.g., traffic impact analysis, freeway facility design, alternatives analysis, interchange modification, corridor studies). (2) Identify the learning objectives for the sample applications by assessing the shortcomings of the current HCM example problems in reflecting real-world analyses. This will involve identifying broad issues to be illustrated through the sample applications (e.g., use of demand rather than volume, oversaturated conditions, problems that cannot be addressed by HCM methodologies, interpretation of results, aggregation of measures of effectiveness). Concerns specific to an individual HCM chapter (e.g., treatment of right turn on red, turn bay overflows and blockages, uneven lane utilization, two-way left turn lanes) should also be identified in this task. (3) From the Task 1 inventory, recommend applications to be included in the guide. Criteria for recommendations should relate to the learning objectives identified in Task 2, likely availability of data, and prevalence of the application in the real world. Several applications should incorporate methodologies from multiple HCM chapters. The HCM calculation methods that will be used within each recommended application should be described as should the methods that will be used to verify the calculation results. Recommendations must consider the project resources available. (4) Submit an interim report to document Tasks 1 through 3 and identify needed changes in the work plan for subsequent tasks for review by the NCHRP. The interim report shall include a proposed table of contents for the handbook. Alternative layouts for the applications shall be presented using an example application. (5) Assemble the data for the sample applications. The data may include photographs, schematic diagrams, vehicular and nonvehicular traffic demands and composition, facility geometry, and traffic control types and parameters. (6) Fully develop the applications. The applications should be tutorial or educational in nature. Each application should include: (a) the learning objectives addressed by the application, (b) description of the application, (c) how the application data were set up for analysis, (d) how the HCM was used including direct references to the HCM text, (e) interpretation and reasonableness checks of the results, and (f) limitations of the HCM methodology for this application. It is expected that a few applications will not be appropriate for analysis using HCM methodologies and general suggestions on a more appropriate approach should be included. Each application can use either metric or U.S. customary units. (7) Submit a brief final report that documents the entire research effort. Submit the guide as a stand-alone document. The guide should be clear and concise for use by practitioners and students.