NCHRP 08-36: Research for The AASHTO Standing Committee on Planning
2009-14
Research Problem Statement for NCHRP 8-36
Title
 Weight vs. No-Weight Vehicle Classification
Problem
 Traffic data collection agencies collect traffic volume, classification, and weigh-in-motion data
for planning and other purposes. Vehicle classification systems classify vehicles based on axle
spacing or vehicle length while weigh-in-motion systems generally make use of weight data in
addition to axle spacing. It is generally believed that weigh-in-motion systems can classify
traffic more accurately by incorporating weight criteria into the classification algorithm. If
there is a significant difference in classification results between axle spacing based algorithms
versus axles spacing plus weight algorithms, this can cause concerns with data users is they see
unexplained shifts in data as well as basic errors in traffic data collection.
Objective
 1. Identify differences in classification counts for axle spacing based algorithms versus axle
spacing plus weight algorithms.
2. Use statistical processes to determine if these differences are significant.
3. Identify traffic conditions (i.e. classification volume distributions) that increase or decrease
this significance.
2. Identify possible ways of making the different algorithms predict more compatible class
counts for different traffic conditions.
Priority
 Classification data is collected for the purpose of transportation planning as well as other uses.
The accuracy (or inaccuracy) of this data can impact decisions that can have significant
ramifications on freight planning, pavement engineering, and safety analysis.
Time and Cost Estimate
 One Year - $85,000
Submitted on behalf of the TRB Highway Traffic Monitoring Committee (ABJ35).
Ralph Gillmann
Travel Monitoring Team Leader
Federal Highway Administration
East Building, HPPI-30
1200 New Jersey Avenue, SE
Washington, DC 20590
2/13/2016