Research for the AASHTO Standing Committee on Planning. Task 89. Evaluating and Communicating Model Results: Guidebook for Planners

Often the division of responsibilities within metropolitan planning organizations (MPOs) relegates travel forecasting to technical experts while use of model output for policy and plan development is in the hands of planners and policy makers. This division of labor can lead to unintended consequences in the decision-making arena. As noted by the Committee for Determination of the State of the Practice in Metropolitan Area Travel Forecasting in the Transportation Research Board's Special Report 288, Metropolitan Travel Forecasting - Current Practice and Future Direction, "There are many sources of error and uncertainty in travel demand forecasting, but end users of most travel forecasts would not be aware of these limitations" (page 85). Also, "In the committee's experience, agencies have reported future-year facility volumes on the basis of data taken directly from the model outputs. Unless the models have been carefully restructured or estimated with the objective of addressing such issues, the resulting forecasts may not be valid". Planners are engaged in increasingly complex decision-making analyses relying on the output of ever-more sophisticated modeling tools, yet they often possess only a cursory understanding of travel forecasting models and their inherent assumptions, biases, and limitations. This heightens the risk that the modeling process or its output will be unintentionally misrepresented or misapplied, with unfortunate consequences for resulting decisions and investments. Transportation planners do not need to be able to develop a travel demand model or conduct a traffic forecast, but they do need a solid understanding of key modeling fundamentals that go beyond recitation of the four-step process. This is true whether the model is developed in-house by agency staff or is contracted to a consultant or outside agency. Planners often act as the liaison between policy makers, the public, and modelers. A stronger foundation in the appropriate applications of forecasting models and the ability to effectively communicate this will strengthen that planning role. This report identifies and describes assumptions, applications, and limitations that transportation planners should understand about both conventional and advanced forecasting models and processes. It should help planning practitioners to better understand the forecasting process, increase their ability to interpret and apply model output effectively, and help them better communicate this aspect of the transportation planning process to policy makers. Transportation planners should be able to (1) ask and answer critical questions about their agencies' models and model development processes; (2) to understand how robust or sensitive the outputs are, why that matters; and (3) incorporate that knowledge into planning and programming decision-making processes.


  • English


  • Status: Completed
  • Contract Numbers:

    Project 08-36, Task

  • Sponsor Organizations:

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590

    American Association of State Highway & Transportation Officials

    444 North Capitol Street, NW, Suite 225
    Washington, DC  United States  20001

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001
  • Performing Organizations:

    Cambridge Systematics, Incorporated

    100 Cambridge Park Drive
    Suite 4000
    Cambridge, MA  United States  02140-2369
  • Principal Investigators:

    Goldfarb, Daniel

  • Start Date: 20090429
  • Expected Completion Date: 0
  • Actual Completion Date: 20100531
  • Source Data: RiP Project 26917

Subject/Index Terms

Filing Info

  • Accession Number: 01557204
  • Record Type: Research project
  • Source Agency: National Cooperative Highway Research Program
  • Contract Numbers: Project 08-36, Task
  • Files: TRB, RiP
  • Created Date: Mar 19 2015 1:00AM