LTPP Data Analysis Task Order 13

Technician measuring traffic speed using radar gun


Many states use classification data in lieu of weight data for pavement designs. The designs, particularly those generated using the mechanistic-empirical pavement design guide (MEPDG) methodology, depend on accurate vehicle classification data.


As part of our 5-year data analysis contract with the Federal Highway Administration (FHWA) Long Term-Pavement Performance (LTPP) program, ARA conducted a detailed study to compare the 13-category vehicle classification scheme used in the LTPP program with schemes currently being used by various states. As part of this study, ARA:

  • Determined how well the LTPP classification scheme is performing across the country.
  • Determined whether the LTPP classification scheme must accurately classify all vehicle types to be useful for pavement research.
  • Recommended necessary changes to the LTPP classification scheme to make it universal.
  • Defined the field of applicability of the LTPP classification scheme. Are certain vehicle classes unambiguous and the same throughout the study area, even if all classes are not?
  • Determined the size and extent of pavement design errors that can be expected when using inconsistent classification schemes for both weigh-in-motion (WIM) and classification counts.
  • Identified which LTPP General Pavement Studies (GPS) sites can use WIM data from Specific Pavement Studies (SPS) sites using the LTPP scheme and developed a software program that guides users to which WIM data can be used to estimate vehicle loads at each of the GPS sites.


The LTPP program has developed and deployed a vehicle classification scheme that is being used at Transportation Pooled Fund Study (TPF) WIM sites across the country. This project examined the performance of that classification scheme and the implications of its use for the development and application of default values for use within the MEPDG. It also provided the enhancements and helped FHWA to finalize the scheme.

Traffic Monitoring

Traffic Monitoring

National-level traffic research; installation and maintenance of traffic counting, classification, and weigh-in-motion systems; data collection... more