In order to gain and sustain public (and legislative) understanding and support for the management and stewardship of their transportation systems, state DOTs, MPOs, transit authorities, and others want to develop and employ system-performance measures that express congestion and mobility in terms that system users can appreciate and understand. There is heightened interest in measures of travel time, delay, and reliability. This interest is based on the need for improved planning and analytical procedures to measure and predict how individual traveler and goods movements will be affected by incidents and other generators of non-recurring delay. There is also a need for measurements that individuals can use to reduce the uncertainty and loss of productivity that occur when system reliability is low. These measures will be appropriate for use in system planning, corridor development, priority programming, and operations (including public information programs) to improve transportation system performance. Such measures also will be useful in management and performance reporting by the responsible agencies.
Use of travel time, delay, and reliability as performance measures is hampered by complex data requirements, data accuracy issues, and inadequate procedures for incorporating these measures into the transportation planning process. One reason that these measures have not been more widely implemented is that they can be expensive and difficult to generate. A relatively small number of public agencies have the data collection programs or analytical forecasting capabilities to generate reliable estimates of these measures. In many states, travel time data are available for relatively few corridors and sample sizes are small. The high costs associated with more comprehensive data collection programs deter many states from investing in such programs. States and MPOs are testing the use of loop detector data and other ITS-collected data to develop travel time, delay, and reliability measures, but these too are fairly sophisticated and, at present, costly efforts.
There is a need for structured, cost-effective measures of travel time, delay, and reliability that can be used by practitioners in predicting, measuring, monitoring, and reporting transportation system performance.
The objective of this project is to develop a guidebook that presents a framework and cost-effective methods to predict, measure, and report travel time, delay, and reliability data from a customer-oriented perspective. The framework will address time of day, transit and highway, passenger and freight, vehicle and user types, and levels of aggregation (such as facility type, functional classification, and system/corridor/segment). The framework will also present and assess 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 evaluation. The methods should be presented in a useful manner for application in a range of settings and complexity.
Accomplishment of the project objective will require at least the following tasks.
(1.) Review current and recent literature and research on travel time, delay, and reliability performance measures. Consider appropriate international and private-sector experience. Include a summary of available information on what transportation customers want relating to system performance in terms of travel time, delay, and reliability. ( 2. ) Conduct a survey of current practice and activities in a variety of transportation research, planning, and operating agencies to assess the state of the practice in the use of travel time, delay, and reliability as performance measures. Identify and distinguish between methods that report on existing travel time, delay, and reliability and those that allow prediction of future reliability under varying scenarios of system utilization, congestion, and conditions. (3.) Develop a synthesis of current research and practice in predicting, measuring, and applying travel time, delay, and reliability, in transportation planning and decision making. Summarize approaches that are sufficiently developed and documented for immediate application by other agencies. Identify needs for further development of more cost-effective methods of data collection, analysis, and measurement. (4.) Conduct a workshop including selected practitioners of state DOTs, MPOs, and other agencies to identify the characteristics of a useful framework and methods for employing travel time, delay, and reliability performance measures. This workshop should provide the opportunity for detailed discussion of problems and potential solutions for data collection, analysis, and performance reporting in transportation planning and decision making. (5.) Develop a conceptual framework and potential methods, covering the scope of the research objective for the use of travel time, delay, and reliability measures for transportation planning and decision making. ( 6.) Prepare and submit an interim report that (1) documents the work performed and findings from Tasks 1 through 5 and (2) describes a preliminary recommended framework and proposed methods for using travel time, delay, and reliability as transportation performance measures. Present the information in the interim report and necessary revisions to the work plan at a meeting of the NCHRP panel. (7.) Based on NCHRP panel guidance from Task 6, prepare an annotated outline of the guidebook for NCHRP panel review. (8.) Adapt, or develop and document, cost-effective methods of data collection, quality assurance, analysis, and modeling. Identify data needs, sources, and gaps. Identify how to use the data and how to communicate results to address customer expectations. (9.) Adapt, or develop and document, methods to link travel time, delay, and reliability measures to transportation planning and decision making. (10.) Develop the framework and methods to be presented in the guidebook for review and comments by the Task 4 workshop participants. (11.) Prepare and submit a final report, including the final guidebook for NCHRP panel review and approval.
This report has been published as NCHRP Report 618 and is available here.