The Value of Better Vehicle Occupancy Estimates for Project Prioritization

Abstract

Transportation projects are increasingly evaluated based on how they improve person throughput, which requires knowing the passenger car occupancy. Yet obtaining occupancies is labor intensive, leading agencies to rely on statewide values. How useful are locality-specific vehicle occupancies? A case study of 38 candidate Virginia highway investments showed an occupancy change of .15 randomly applied to one-half of the projects affects 24% to 42% of project rankings if locality-specific occupancies are used. Occupancy is not the only data element affecting project prioritization, but it is an underlooked one. The study showed that an occupancy uncertainty of .15 is equivalent to an uncertainty of 3.90% in the discount rate or 13.2% in assigned traffic volume. As these investments had a mean value of $17 M, this study demonstrated that when project prioritization metrics are based on person throughput, city-or county-specific occupancies are an integral component of a data-driven prioritization process.