Assessing Passenger Car Equivalency Factors for High Truck Percentages

Trucks, also referred to as heavy vehicles, have an effect on the quality of traffic flow on a roadway. The impact that trucks have is generally attributed to specific differences in 1) the average space taken up by a truck which is greater than that taken up by a passenger car (e.g. average gaps in front of and behind trucks are larger than those associated with passenger cars), and 2) the operational characteristics - acceleration, deceleration, maneuverability, etc. of trucks are different from those of passenger cars. The Highway Capacity Manual (HCM) analysis and design procedures utilize Passenger Car Equivalents (PCE), also called equivalency factors, to account for the presence of trucks in a traffic stream. Using these PCEs, a heterogeneous mix of vehicles in a traffic stream can be expressed as a standardized homogenous traffic stream of passenger cars. Essentially, the PCE of a truck represents the number of passenger cars that would have an equivalent effect on the quality of the traffic flow (Webster and Elefteriadou 1999). These PCEs are considered important in carrying out most traffic analyses. The Nebraska Department of Roads (NDOR) management adopts Highway Capacity Manual (HCM) methods in their Interstate widening scheduling tool. An important input for the tool is the passenger car equivalent (PCE) variable that is provided as a function of truck proportions in the traffic stream. However, PCE values in the HCM are limited to truck proportions of 25 percent. In Nebraska, there are road sections where the percent of trucks is greater than 25 percent and therefore the decision making process of the Interstate widening scheduling tool is somewhat questionable. The objective of this research is to accurately determine passenger car equivalents for basic freeway segments in Nebraska. The particular condition of concern for Nebraska is the high percentage of trucks and other heavy vehicles using Interstate 80 in the western regions of the state.


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    • Status: Active
    • Contract Numbers:

      SPR-P1(15) M023

    • Sponsor Organizations:

      Federal Highway Administration

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

      Nebraska Department of Roads

      P.O. Box 94759
      Highway Building
      Lincoln, NE  United States  68509-4759
    • Performing Organizations:

      University of Nebraska, Lincoln

      527 Nebraska Hall
      Lincoln, NE  United States  68588-0529
    • Principal Investigators:

      Rilett, Laurence

    • Start Date: 20140701
    • Expected Completion Date: 0
    • Actual Completion Date: 20170228
    • Source Data: RiP Project 36236

    Subject/Index Terms

    Filing Info

    • Accession Number: 01560309
    • Record Type: Research project
    • Source Agency: Nebraska Department of Roads
    • Contract Numbers: SPR-P1(15) M023
    • Files: RiP, STATEDOT
    • Created Date: Apr 11 2015 1:01AM