Volume 1: Concepts

Chapter 1: HCM User’s Guide

Chapter 1, HCM User’s Guide, is the starting point for learning how to use this edition of the HCM. This chapter presents the purpose, objectives, intended use, and target users of the HCM 2010; describes the contents of each of the four volumes that make up the HCM; summarizes the major changes that have been made to HCM2000 methodologies; and mentions some of the important companion documents to the HCM. The remainder of Volume 1 presents the fundamental information with which users should be familiar before starting to apply the manual.

Chapter 2: Applications

Chapter 2, Applications, introduces the wide range of potential HCM applications, all of which can be applied as stand-alone analyses or in support of a broader process.

Chapter 3: Modal Characteristics

Chapter 3, Modal Characteristics, introduces some basic characteristics of the four major modes addressed by the HCM. The following characteristics are considered in this chapter for each mode:

  • Factors that contribute to a traveler’s experience during a trip,
  • Observed seasonal and daily variations in travel demand,
  • Types of transportation facilities employed by a given mode,
  • Notable capacity and volume observations, and
  • Descriptions of the interactions that occur between modes.
Chapter 4: Traffic Flow and Capacity Concepts

Chapter 4, Traffic Flow and Capacity Concepts, describes how these basic relationships apply to the four modes covered by the Highway Capacity Manual (HCM): automobiles, pedestrians, bicycles, and on-street transit. Details of these relationships specific to automobiles operating on a particular system element (for example, speed– flow curves for freeways) are provided in the appropriate methodological chapters of Volumes 2 and 3.

Chapter 5: Quality and Level-Of-Service Concepts

Chapter 5, Quality and Level-of-Service Concepts, presents the concepts that the Highway Capacity Manual (HCM) uses to describe performance from the traveler point of view in a way that is designed to be useful to roadway operators, decision makers, and members of the community.

Chapter 6: HCM and Alternative Analysis Tools

Chapter 6, HCM and Alternative Analysis Tools, begins by describing the HCM-based tools available to the analyst. In an operations-level analysis, which is one such tool, HCM methodologies are applied directly and the user supplies all required inputs to the procedure. Many planning, preliminary engineering, and design applications do not require the level of accuracy provided by an operations analysis and substitute default values for some (or nearly all) of a methodology’s inputs. Generalized service volume tables are sketch-planning tools that provide an estimate of the maximum volume a system element can carry at a given level of service (LOS), given a default set of assumptions about the system element. The use of local default values and local generalized service volume tables helps reduce the uncertainty in the results of analyses that use these tools, compared with using the HCM’s national default values and tables. The chapter’s two appendices provide guidance on developing local default values (Appendix A) and generating local generalized service volume tables (Appendix B)

Chapter 7: Interpreting HCM and Alternative Tool Results

Chapter 7, Interpreting HCM and Alternative Tool Results, begins with a discussion of the uncertainty in model outputs that results from (a) uncertainty in a model’s inputs, (b) uncertainty in the performance measure estimate produced by a model, and (c) imperfect model specification, in which a model may not fully account for all the factors that influence its output. Uncertainty in model inputs can result from the variability of field-measured values, from the uncertainty inherent in forecasts of future volumes, and from the use of default values. The accuracy of a model’s results is directly related to its uncertainty. A model that incorporates more factors may appear on the surface to be more accurate, but if the inputs relating to the added factors are highly uncertain, accuracy may actually be decreased. Analysts should also carefully consider the precision used in presenting model results to avoid implying more accuracy than is warranted.

Chapter 8: HCM Primer

Chapter 8, HCM Primer, is written for a nontechnical audience and is a synopsis of Volume 1 of the HCM. An example of a potential audience for this chapter is decision makers who may be presented with the results of HCM analyses for the purpose of establishing policy or public interest findings. The chapter covers basic traffic operations terminology, capacity and quality-of-service concepts, and guidance on applying the results of analyses produced by the HCM and alternative traffic operations tools.

Chapter 9: Glossary and Symbols

Chapter 9, Glossary and Symbols, defines the terms used in the Highway Capacity Manual (HCM) and presents the symbols and abbreviations used in the manual. Highway transportation terminology has evolved over time to create multiple definitions, and the confusion has been compounded by technical jargon. The definitions, abbreviations, and symbols presented here are intended to establish a consistent terminology for use in the HCM. It is recognized that other definitions and usage could exist.

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