The National Academies

NCHRP 03-39(2) [Completed]

On-Site Evaluation and Calibration Procedures for Weigh-In-Motion Systems

  Project Data
Funds: $247,846
Research Agency: Washington State University
Principal Investigator: A. T. Papagiannakis
Effective Date: 3/10/1994
Completion Date: 12/9/1995

State highway agencies need accurate truck-weight data for use in planning, design, operations, maintenance, and management activities for both pavements and bridges. Weigh-in-motion (WIM) is the process in which the dynamic tire forces of a moving highway vehicle are measured and then used to estimate wheel, axle, and axle-group loads and gross-vehicle weight. The accuracy of WIM-estimated loads is influenced by site condition, sensor reliability, and other factors. The American Society for Testing and Materials (ASTM) has defined the tolerance (allowable variation from a true value) for WIM-estimated loads and weights for various applications, such as collecting statistical data or screening suspected weight violators from the traffic stream for truck-weight enforcement.

Various WIM systems are available that collect truck data more efficiently than conventional weighing methods. A number of states are currently installing these systems and are specifying and conducting independent acceptance and validation procedures. However, nationally recognized procedures do not exist for on-site evaluation and calibration of WIM systems. Such procedures need to be developed and validated by statistically designed field experiments so that WIM users can be confident that estimated weights will meet tolerances specified for various applications. Widely accepted procedures will also benefit manufacturers by establishing more consistent testing practices by their customers.

An earlier study, NCHRP Project 3-39, Evaluation and Calibration Procedures for Weigh-in-Motion Systems, addressed many relevant issues. However, additional research is needed to develop nationally recognized procedures for on-site evaluation and calibration of WIM systems.

The objective of this research is to develop a program for on-site evaluation and calibration of WIM systems. This research will include identifying calibration algorithms to improve WIM system performance and evaluating the feasibility of using test trucks, simulation techniques, and vehicles equipped with automatic vehicle identification (AVI) for on-site calibration of WIM systems.

Accomplishment of this objective will require at least the following tasks. (1) Review evaluation and calibration procedures previously developed by the NCHRP and other research. Define specifications, operational procedures, and test methods for a program for evaluating WIM systems. Within 3 months, submit an interim report presenting the results of this task for review by NCHRP. A revised version that incorporates reviewers' comments shall be submitted. (2) Review and evaluate available WIM calibration algorithms, identify changes to improve WIM system performance, and recommend improved algorithms for at least six vehicle types. These algorithms shall be incorporated in Tasks 3 and 4. (3) Using available data, evaluate existing computer simulation models to determine the feasibility of using test trucks and simulation techniques for on-site evaluation and calibration of WIM systems that meet the requirements for Types I and II as defined in ASTM E 1318, Standard Specification for Highway Weigh-in-Motion (WIM) Systems with User Requirements and Test Method. It is envisioned that selected test trucks along with simulation will be used. Use of vehicles selected at random from the traffic stream is not recommended. (4) Assess the feasibility of evaluating and calibrating WIM systems by continuously monitoring AVI-equipped vehicles and correlate these results with data obtained from reference measuring devices, such as static scales and other WIM systems. Address the feasibility of implementing such calibration techniques in states where AVI facilities are not available. (5) Demonstrate applicability of the findings of Tasks 3 and 4 by conducting a field test that involves two or more contiguous states. Analyze the cost and operational effectiveness of the on-site evaluation and calibration procedures evaluated in these tasks. Based on test results, refine the WIM calibration algorithms developed in Task 2. (6) Submit a final report that documents the entire research effort. The report shall include practical recommendations for on-site evaluation and calibration of WIM systems together with improved calibration algorithms and an implementation plan for moving the results of this research into practice.

Status: The research has been completed. A summary of the research findings was published as NCHRP Research Results Digest 214, "On-Site Evalutation and Calibration Procedures for Weigh-In-Motion Systems."

To create a link to this page, use this URL: http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=781