Introduction

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The Highway Capacity Manual Applications Guidebook (HCMAG) is intended to assist transportation professionals with the appropriate use and interpretation of the analysis methodologies contained in the Highway Capacity Manual. It uses actual case studies as a means of educating practitioners on how to properly apply these methodologies and when to use alternative means of analysis and evaluation. Each case study begins with a description of one or more interconnected transportation facilities located somewhere in the United States. As part of this description, a number of performance-related issues and problems are identified that require resolution, and these are translated into a series of problem statements subsequently addressed in sequential order. The problem discussions provide detailed information on such issues as data requirements, selection of an appropriate analysis procedure, evaluation and interpretation of the analysis results, and  next steps.

The HCMAG aims to provide specific guidance to users of the Highway Capacity Manual (HCM) in defining and scoping the problems that are to be addressed, identifying and using the appropriate analysis procedures, and tools, and interpreting the analysis results and understanding what they mean. Within the definition and scope of the problem, the HCMAG provides guidance in identifying the appropriate parts of the transportation system that should be included, the most appropriate performance measure to focus upon, the available and appropriate tools for application, the manner in which solution alternatives can affect the problem definition, and the types and quantities of data that will be required. With respect to the analysis applications and tools, the HCMAG provides guidance in identifying application steps where special care and attention is appropriate, understanding how multiple HCM analysis methodologies are consistent (or inconsistent) with one another, and recognizing the conditions under which the application of analysis tools outside the purview of the HCM may be warranted. Finally, the HCMAG provides guidance in the analysis and interpretation of results by assisting the user in determining whether the results are reasonable and consistent, understanding why sensitivity analysis is important and how to conduct a sensitivity analysis, determining what solution alternatives are feasible, learning how to present the results to decision makers in a concise and understandable fashion, and recognizing the possible next steps in the investigation that the analysis results point toward.

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The HCMAG includes some discussion of basic concepts and terminology (for example, signal phase sequencing nomenclature), but presumes the user is already familiar with these concepts and has access to generally-used resource documents like the Manual on Uniform Traffic Control Devices and the American Association of State Highway Transportation Officials (AASHTO) Policy on Geometric Design. It also presumes the user has access to the HCM, and therefore does not repeat the step-wise application technique for each analysis methodology that is already described in the HCM.

This Guidebook is intended to be a supplemental resource document to the HCM that can be used in a variety of ways:

As a companion tool to the HCM, commercial software is available to perform the numerical calculations for the analysis procedures. All of the HCM computational results presented in the HCMAG were produced and independently verified by at least two widely distributed software products that purport to implement the HCM procedures faithfully. In all cases where HCM procedures were applied, the analysis results are presented in a software-independent format, reflective of the fact that the HCMAG does not and cannot judge the fidelity of any software package.

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The case studies contained in the HCMAG also include some situations where the desired study of performance in a traffic situation is not explicitly covered by the HCM analysis methodologies, or where the traffic situation is very difficult to analyze using empirical and analytical models. A variety of additional software packages are available to assist the user in the analysis of these situations. Where such cases arise, the HCMAG explicitly identifies the particular software package that was used so that the user has an appropriate context in which to view the output and understand the ensuing discussion. It must be emphasized that the particular software used in the HCMAG is applied for illustrative purposes only, and its use within the HCMAG case studies does not imply any endorsement or judgment relative to other software packages that can also be applied with equal effectiveness to conduct similar analyses. It should also be noted that software packages are typically updated and refined quite frequently, so the particular output results reported in the HCMAG may not be replicable with the latest version of the software. This is not considered to be a significant problem for the HCMAG where the focus is more upon the analysis process and the interpretation of the results, and less upon the particular results obtained.

Ultimately, the HCMAG is intended to address every facility type referenced in the Highway Capacity Manual. Initially, however, this first edition of the HCMAG is more limited in its focus. To ensure that the HCMAG provides the most effective guidance to the widest range of potential users, its initial focus is toward those applications that typically receive the most attention and activity from the HCM user community. These include:

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Multimodal interactions and considerations are addressed within the HCMAG in the context of these five facility types. The HCMAG also identifies and discusses interactions that occur between adjacent components of the transportation system, such as the operational effects of installing a new traffic signal on an arterial with pre-existing upstream and downstream signalized intersections. It is anticipated that future versions of the HCMAG will be expanded to address more comprehensively the other facility types contained in the HCM.

All analyses within the HCMAG are conducted in U.S. Customary units, reflecting the continuing predominant use of these analysis units throughout the United States. This should not have any great bearing on the overall usefulness of the Guidebook, whose overarching purpose is to increase user understanding of the appropriate application of HCM procedures and the appropriate interpretation of the results.

How to Navigate the HCMAG

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The HCMAG has been designed so that it can be used most effectively as an electronic document. Because it uses HTML format, the HCMAG should be viewed and navigated with a web browser such as Internet Explorer or Netscape. Moving forward or backward through the document can be accomplished by clicking on the  [Continue] or [Back] hyperlinks located near the upper left-hand and bottom right-hand corner of every page. The forward (à) and back (ß) arrows on the menu bar of the web browser can be used to retrace the user’s previous steps through the document.

In addition to the viewing and navigation tools normally available on the web browser itself, the HCMAG also incorporates some other navigational aids that are intended to assist the user in quickly identifying and accessing information that is relevant to his/her specific needs. The remainder of this section introduces and describes these additional navigational aids in greater detail.

How to Move Between Case Studies

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The home page of the HCMAG document serves as the primary transfer point for moving among the various case studies. At the top of the home page is a set of index tabs, each of which is associated with a particular chapter of the HCMAG. Resting the mouse over any one of these tabs will reveal a further text description of the contents of the associated chapter. A single mouse click on the tab will transfer the user to the first page of the chapter.

All the pages within each chapter have a common header at the top of the page that identifies the chapter title. In the upper left-hand corner of this header are the words “HCMAG”; a single mouse click on these words will transfer the user back to the home page of the HCMAG document.

Each page of the chapter also displays a chapter index, in column format, on the far left-hand side of the page. A single mouse click on “HCMAG Home”, which is located at the very top of this chapter index, will also transfer the user back to the home page of the HCMAG document.

How to Navigate Within a Chapter

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Inside each chapter, there are many ways for each user to navigate among its various parts. The chapter’s table of contents, which is displayed in column format on the far left-hand side of the page, is probably one of the most powerful ways to navigate. A single mouse click on any one of the entries in this table of contents will transfer the user to the first page of that chapter section. The user can always determine his/her current location within the chapter by looking at the side-bar table of contents: the chapter section within which the user is currently located will appear as the only depressed button within the table of contents.

As the user proceeds through the pages that make up any particular chapter section, a header near the upper left-hand corner of the page will identify the current chapter section, the current page number, and the total number of pages within the chapter section. On the left side of this header is a hyperlink, identified with the word “Home”, that will take the user back to the beginning page of the chapter section whenever it is pressed. Near the bottom right-hand edge of each page are two hyperlinks, [Back] and [Continue], that will move the user, respectively, to the previous page or to the next page of the chapter section. On the first page of each chapter section, the [Back] hyperlink will transfer the user to the first page of the previous chapter section, or to the home page of the HCMAG if the current chapter section is also the first section of the chapter. On the last page of each chapter section, the [Continue] hyperlink will transfer the user to the first page of the next chapter section, or to the first page of the next chapter if the current chapter section is also the last section of the chapter.

The chapter table of contents, located on the left-hand side of each chapter page, also includes hyperlinks to a few other locations that might be of regular interest to the user.

Format of Each Case Study

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Each case study is organized similarly:

The introductory sections are designed to acquaint the reader with the important characteristics of the case study, including the transportation facilities of interest, the relevant traffic characteristics, the surrounding land uses, the key stakeholders and their issues of concern, and the general scope of the investigation that is about to be undertaken. These sections also provide an overview of the analyses that will be undertaken later in the chapter. Based on this, they also discuss the range of possible analysis tools and their associated data requirements. This discussion leads to the identification of the particular analysis tools that will be applied to the subsequent problems in the chapter.

Each problem is separately discussed, and in many cases more than one analysis must be conducted to address all the issues the problem raises. Thus, each problem is typically associated with several sub-problems, each of which constitutes the application of a single analysis procedure. Within each sub-problem, the information necessary to conduct the analysis is presented, along with the analysis results. The step-wise application of the analysis procedure is conducted through use of appropriate software and is not explicitly discussed in the HCMAG. This avoids repetition of information already available and published in the HCM and/or software reference manuals.

The analysis and discussion sections of each case study expand upon the findings of each analysis and problem to identify the key insights that have emerged and the important conclusions that can be reached. Within this section, the HCMAG critically reviews the results to ensure that they are reasonable, meaningful, and consistent. It may also deal with issues of sensitivity analysis, the feasibility of the recommended solutions, methods for presenting results to decision makers, and possible next steps.

Searching for Information

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Search Engine (on-line version only)
A search engine is available in the on-line version of the HCMAG that greatly facilitates the reader’s ability to locate information related to specific key words and phrases.

Overview index of problem contents
The first section of each chapter contains a graphic that identifies, in tabular format, the types of HCM analyses that are addressed within the chapter. Each column within the table highlights a defining characteristic that can be used to describe the types of HCM analyses performed:

Within each column is a listing of the possible values that can be associated with the characteristics. The kinds of problems that are addressed in the chapter, within each of the seven categories listed above, are highlighted in blue so that the reader can easily identify them. This provides a concise visual summary of the kinds of problems and types of analyses that are addressed within the case study.

How to Print a Hardcopy Version of a Case Study

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Although the HCMAG has been designed and written primarily for use in an electronic environment, it is also possible to create a hardcopy version of each case study. To do so, the user must enter into the particular case study and the particular chapter section for which a hardcopy is required. A printer icon will be located in the upper left-hand area of the page, and associated with the printer icon will be some text identifying the particular chapter sections that can be converted into a printable form. Clicking on this icon or the associated text will cause a printable version of the chapter section(s) to be printed, and the user will be asked to identify the appropriate printer to which the print file should be directed.

It is important to note that each icon is associated with only one or a few of the chapter sections associated with the case study. If it is desired to generate a hardcopy version of the entire case study, then the user must repeat this process for each chapter section for which there is a separate printer icon. The individual printouts that results from this process can then be combined into a single complete document.

Naturally, the printed version of each case study or chapter section will not be able to display many of the dynamic elements that are an inherent part of the electronic version. Thus, information that is available through pop-up windows or multimedia elements will not be viewable in the printed version.

How to Download Problem Datasets

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The datasets that form the basis for each of the HCM analyses are available for download so that the user can explore them in greater detail using a variety of different software packages. Each dataset has been translated into XML format, which can be imported directly into many different software packages. Hyperlinks to these datasets can be found at two different locations:

Right-clicking on the hyperlink to the appropriate data set will allow the user to download the dataset file in XML format, and to save the file locally. The text strings that make up the XML format can then be imported directly into a variety of software packages implementing the HCM methodologies.

Where to Go to Report Problems or Ask Questions

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If you encounter a problem in using or navigating through the HCMAG, or if you have a question about the site or its contents, then we encourage you to click on the following link to contact the support center.