Evaluation of WIM Auto-Calibration Practices and Parameters

Weigh-in-Motion (WIM) systems capture weight and axle configurations of vehicles using the state highway network. This data serves as valuable and essential input for evaluating the performance of the transportation infrastructure. In particular, WIM data is needed to support Federal truck size and weight regulations, and to design, maintain, and preserve pavements. To produce accurate weights, sensors must be calibrated at installation and at regular intervals following the procedures outlined in ASTM E1318. Poor scale calibration can lead to significant errors in determining the load on the pavement: a 10% over-estimation in axle weight results in 45% over-estimation of Equivalent Single Axle Loads (ESALs). On-site calibration requires repeated passes over the sensors of test vehicles with known weights. This is a time consuming and expensive process. Therefore, several states have adopted auto-calibration procedures developed by WlM vendors. Since auto-calibration does not require the use of test trucks, it is less costly than on-site calibration with test trucks. Auto-calibration is an algorithmic procedure by which weights measured by the WIM sensor are adjusted based on tunable parameters set by the WlM vendor. A common method of auto-calibration is to adjust the calibration factor based on assumed Front Axle Weights (FAW) of a sample of five-axle tractor-trailers that pass the site in a given hour. However, auto-calibration functions are only effective with a complete understanding of site-specific traffic characteristics like average vehicle and axle weights and traffic volumes by vehicle class. Thus, this study will develop a protocol for determining how best to collect site-specific characteristics to update the auto-calibration functions at the Arkansas WIM sites. This will ensure that truck size and weight measurements gathered from WIM accurately reflect the loads and configurations of trucks traversing Arkansas highways.


    • Status: Active
    • Funding: $174545
    • Contract Numbers:


    • Sponsor Organizations:

      Federal Highway Administration

      1200 New Jersey Avenue, SE
      Washington, DC  United States  20590
    • Managing Organizations:

      Arkansas State Highway and Transportation Department

      P.O. Box 2261
      Little Rock, AR  United States  72203
    • Project Managers:

      Caster, William

    • Performing Organizations:

      University of Arkansas, Fayetteville

      4190 Bell Engineering
      Civil Engineering
      Fayetteville, Arkansas  United States  72701
    • Principal Investigators:

      Hernandez, Sarah

      Nurre, Sarah

    • Start Date: 20170726
    • Expected Completion Date: 20190125
    • Actual Completion Date: 0

    Subject/Index Terms

    Filing Info

    • Accession Number: 01678322
    • Record Type: Research project
    • Source Agency: Arkansas State Highway and Transportation Department
    • Contract Numbers: TRC1801
    • Files: RiP, STATEDOT
    • Created Date: Aug 22 2018 3:11PM