A Framework for Improving Travel Time Reliability

Seven major factors account for approximately half of all traffic delay, and therefore, a great deal of the uncertainty associated with travel time: (1) traffic incidents, (2) weather, (3) work zones, (4) fluctuations in demand, (5) special events, (6) traffic control devices, and (7) inadequate base capacity. These factors often interact, which increases the challenge of reducing the uncertainty of travel time that drivers experience. The overall goal of the SHRP 2 Reliability program is to reduce non-recurrent congestion through incident reduction, management, response, and mitigation of the contributing root causes. Achieving this goal would significantly improve travel time reliability for many types of person and freight trips on the nation’s highways. Travel time reliability refers to how travel time varies over time and the impacts of this variance on highway users. In other words, for repeated travel or vehicles traveling the same route, there is an underlying distribution of travel time for a particular trip between two points within a specific time period. Individual travelers respond differently to the factors and uncertainties associated with the travel time. So do those involved in freight transportation. For important trips, such as a trip to the doctor or a just-in-time freight delivery, drivers will build extra time into the trip to ensure a high probability of arrival within a time window. Travel time reliability is a new and complex topic to measure highway system operational performance and provide assistance for individual personal and freight travel decisions. The research will report the contributing impacts of the primary factors that cause unreliability and present a wide range of effective mitigation measures to counteract these factors. Decision makers will be able to select system operational measures, as an alternative to system expansion, to improve travel reliability, in many cases, at reduced cost and in short time frames. This framework would consolidate the project findings to provide decision makers and practitioners a guide to understand travel time reliability, incorporate reliability in project planning and promote the merit of systems operations and management solutions to prevailing problems. The major objective of SHRP 2 Reliability research is to greatly improve the reliability of highway travel times by reducing the frequency and effects of events that cause travel times to fluctuate in an unpredictable manner. The results of the research program should help local, state, and national agencies reduce travel time variability for travelers and shippers. The Reliability research plan addresses both recurring and nonrecurring congestion with an emphasis on nonrecurring congestion. The following seven potential sources of unreliable travel times (i.e., events that cause variable travel times) were identified: traffic incidents, work zones, demand fluctuations, special events, traffic control devices, weather, and inadequate base capacity.


  • English


  • Status: Proposed
  • Funding: $1800000.00
  • Contract Numbers:

    Project L17

  • Sponsor Organizations:

    Strategic Highway Research Program 2

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC    20001
  • Project Managers:

    Plazak, David

  • Start Date: 20090314
  • Expected Completion Date: 0
  • Actual Completion Date: 0
  • Source Data: RiP Project 21420

Subject/Index Terms

Filing Info

  • Accession Number: 01462158
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project L17
  • Files: TRB, RiP
  • Created Date: Jan 3 2013 1:59PM