Turner-Fairbank Highway Research Center

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Developing Vehicle Occupancy Factors and Percent of Non-Single Occupancy Vehicle Travel

Product Type

Research Report


Robert Krile, Andrew Landgraf, and Elizabeth Slone




Vehicle occupancy factors (VOF) and percent of non-single occupancy vehicle (NonSOV) travel are important considerations for transportation planners and policy makers. A methodology is proposed to estimate VOF and NonSOV based primarily on police records of occupancy from crashes. These data may be biased due to non-representativeness of occupancy in crashes compared to that of all driving. The bias is proposed to be corrected with post-stratification weighting and an occupancy bias correction from historical data. VOF and NonSOV were estimated for 10 years for all states and urbanized areas with a population of at least 200,000 using national records from the Fatality Analysis Reporting System (FARS). Crash records from individual states were utilized for estimates of seven pilot states and their urbanized areas. Validation checks were conducted for these estimates. The computer code used to generate the estimates is provided. The development of credible VOFs and NonSOV from crash records was accomplished on this task. There were certain limitations to the approach that could not be immediately overcome and some potential future limitations. With appropriate documentation of these issues, the general methodology is recommended to be implemented with state-based crash records as the primary source, where available, and the FARS system otherwise.

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Vehicle occupancy factor
non-single occupancy vehicle travel

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