Heavy Vehicle Performance During Recovery From Forced-Flow Urban Freeway Conditions Due To Incidents, Work Zones and Recurring Congestion

Information contained in the Highway Capacity Manual on the influence heavy vehicles have on freeway traffic operations has been based on few field data collection efforts and relied mostly on traffic simulation efforts. In the 2010 Manual heavy vehicle impact is evaluated based on “passenger car equivalent” values for buses/trucks and recreational vehicles. These values were calibrated for relatively uncongested freeway conditions (levels of service A through C) since inadequate field data on heavy vehicle behavior under congested conditions were available. Field-collected headway information was based on the average headway for vehicles in a particular class, regardless of the type of vehicle they were following. The goal of the present effort was to collect and analyze freeway field data on headways with an emphasis on heavy vehicle behavior under lower speeds typically associated with a level of service E (capacity) or F (forced-flow conditions). Contrary to previous efforts incorporated in the Highway Capacity Manual methodology, that disregarded the effect a leading vehicle has on headways, headway information was collected for ten leading/following vehicle pair types containing at least one passenger car (for example buses followed by passenger cars). Headway statistics were analyzed for nine speed ranges (up to 20 mph; 20-25 mph; 25-30 mph; 30-35 mph; 35-40 mph; 40-45 mph; 45-50 mph; 50-55 mph; and 55+ mph) and ten vehicle pair types. Passenger car equivalent values were derived for each speed range based on the average headway for a specific vehicle pair type divided by the average headway between passenger cars. A total of 3,981,810 individual vehicle records were used to construct the 2,645,210 vehicle pair records for which headway statistics were compiled. All analyzed information originated from the Milwaukee County, Wisconsin urban freeway system. Leading and following vehicle class and speed were found to significantly influence headways and passenger car equivalent values.

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  • Supplemental Notes:
    • This document was sponsored by the U.S. Department of Transportation, University Transportation Centers Program.
  • Corporate Authors:

    National Center for Freight and Infrastructure Research and Education (CFIRE)

    University of Wisconsin, Madison
    1415 Engineering Drive, 2205 Engineering Hall
    Madison, WI  United States  53706

    Research and Innovative Technology Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Authors:
    • Drakopoulos, Alex
    • Liu, Yue
    • Horowitz, Alan
  • Publication Date: 2013-12


  • English

Media Info

  • Media Type: Digital/other
  • Edition: Final Report
  • Features: Appendices; Figures; References; Tables;
  • Pagination: 106p

Subject/Index Terms

Filing Info

  • Accession Number: 01534893
  • Record Type: Publication
  • Report/Paper Numbers: CFIRE 04-17
  • Contract Numbers: 244K672
  • Created Date: Aug 20 2014 3:37PM