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1 SUMMARY Cost-Effective Performance Measures for Travel Time Delay, Variation, and Reliability Introduction This guidebook presents a framework and cost-effective methods to estimate, predict, measure, and report travel time, delay, and reliability performance data. The framework is applicable to highway vehicular traffic and also can be used for highway-carried public transit and freight vehicles. The guidebook presents and assesses performance measures currently believed to be most appropriate for estimating and reporting travel time, delay, and reliability from a perspective that system users and decision makers will find most understandable and relevant to their experience and information needs. This guidebook also presents various data collection methods, analysis approaches, and applications that most effectively support transportation planning and decision making for capital and operational investments and for quality of service monitoring and evalu- ation. Methods are presented in a manner to be useful for application in a range of settings and complexity, but are not intended to support real-time applications of travel-time data such as Traveler Information programs. Organization The guidebook begins with an introductory chapter (Chapter 1) that sets the context and provides an explanation of why performance measurement is an important agency prac- tice, and how travel-time-based measures can improve the planning process and results. This first chapter provides useful methods and advice, regardless of the specific application, such as how agencies can use performance data to affect decisions and the choices between alternatives more clear, or selecting methods for reporting results appropriate for various planning and decision-making situations. The technical core of the guidebook is the remaining Chapters 2 through 8. Chapters 2 and 3 describe specific performance measures, as well as methods and procedures for data collection and processing. Chapters 4 through 7 describe fundamental applications that the analyst will invariably tackle, such as before/after studies or alternatives analyses. Chapter 8 provides guidance on reporting performance results, and on using travel-time-based measures in a variety of standard planning and decision-support situations that incorporate the fundamental techniques and applications from Chapters 4 through 7. The paragraphs below provide a more detailed overview of each of the chapters in the guidebook. 1. Introduction. This chapter describes the purpose and scope of the guidebook, intended users, and the audience, those who must eventually understand the results and make or influence decisions based on those results. Included is a discussion of travel time, delay, and reliability in transportation systems, and intended applications for the guidebook. Necessary definitions
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2 and nomenclature with enough background and history to establish the foundation and continuity of this guidebook is provided. This introductory chapter contains several key sections: Why Measure Travel-Time Performance? The rationale and sales pitch for the use of travel-time-based measures in planning and decision-making. Discuss the various aspects of measurement, such as trip-based versus vehicle-based measures, relevance to freight movements, and how the guidebook will address modes other than autos on freeways and highways. How to use the guidebook. A description of the information contained here, the organiza- tion of the information, and a recommended approach to using the guidebook. Limitations of the guidebook. A few key caveats regarding uses for which the manual is not intended (e.g., traveler information or public relations programs). Measuring Mobility and Reliability. An overview of the key steps involved in using travel-time-based measures to define and predict system performance, and how to approach the use of such measures in a planning situation. 2. Selecting Performance Measures. What should influence the selection of measures for a given application; relative importance and sequence of agency goals and objectives in deter- mining appropriate measures. We provide a checklist of considerations for measure selec- tion, a quick reference guide to selected measures, and detailed discussion and derivation of the most useful measures that define mobility (in terms of travel time and delay) and relia- bility (in terms of variability in travel time). 3. Data Collection and Processing. This chapter provides guidance on the development of a data collection and sampling strategy for measuring travel time in the field and for managing data quality. It describes how to compute the mean and variance of travel time and delay. It also describes how to compute the basic components of reliability metrics. 4. Before/After Studies. This chapter describes how to solve special issues involved in evaluating the effectiveness (in the field) of measures to reduce travel time, delay, and variability. 5. Identification of Deficiencies. This chapter describes how to identify travel time, delay, and reliability deficiencies from field data and distinguish actual deficiencies from random variation in the field data. A diagnosis chart is included to assist in identifying the root causes of travel time, delay, and reliability deficiencies. 6. Forecast/Estimate Travel Time. This chapter provides procedures for estimating travel time, delay, and reliability from travel volumes. This information is presented to allow prediction of future conditions where a travel model is used to generate future demand volumes, and to accommodate the many agencies that currently do not have continuous data collection processes on the system or facilities they wish to measure. 7. Alternatives Analysis. This chapter provides guidance on the generation and evaluation of alternative improvements for reducing travel time, delay, and variability. 8. Using Travel-Time Data in Planning and Decision Making. This chapter provides guid- ance and examples of effective methods for presenting the results of travel time, delay, and reliability performance analysis or forecasts. This chapter also describes the specific steps for using quantitative travel-time performance data to support decisions about transportation investments, using six typical planning applications to illustrate the process for developing and incorporating information into the planning process. Limitations The primary intended use of this guidebook is to support planning and decision making for transportation system investments, including capital projects and operational strategies. The level of precision of the methods is consistent with the precision and accuracy of data
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3 typically collected or generated to support planning activities; for example, periodic data collection and use of computer-based forecasting models to estimate future demand for potential system improvements. The procedures here are intended to support a higher-level screening and analysis process to identify needs and deficiencies and to evaluate potential solutions for meeting needs or correcting deficiencies.