Person Occupancy

How well-utilized are the vehicles traveling on the transportation network?

Person occupancy estimates how many people are served by the vehicles they use on the network and can help to understand travel patterns and how many people are being served, as opposed to just knowing how many vehicles are being moved through a given corridor. Efforts to encourage carpooling behavior can also be evaluated using this metric.

Person OccupancyPersons per vehicle (PMT/VMT)Identify Needs

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*sometimes applicable, refer to metric description for more information
  • What? Evaluating the ratio of people per vehicle or the ratio of person miles traveled to vehicle miles traveled provides insight into how efficiently existing vehicle travel moves people. (Note that WSDOT measures person miles traveled that are reliable as one of its MAP-21 performance measures.)
  • Why? Increasing the number of occupants per vehicle increases the network’s efficiency without additional investment.
  • Where? This metric is most relevant for studying highway corridors where performance may be affected by changes in vehicle occupancy influenced by ridesharing or transit use. This measure could also be used where parallel transit facilities increase person throughput or reduce the growth in vehicle traffic on state facilities.
  • How? For existing conditions, conduct vehicle occupancy counts or use WSDOT’s average vehicle occupancy tool to estimate the number of persons in each vehicle, which can be scaled to person throughput using a traffic count. For future conditions, use existing collected vehicle occupancy counts or output from the average vehicle occupancy tool and multiply against the vehicle volume outputs from a travel demand model or growth factor forecast to estimate person throughput based on vehicle occupancy.
Persons per vehicle (PMT/VMT)
Household travel survey data

Calibrated travel model

Vehicle occupancy counts

WSDOT vehicle and heavy truck count database

Transit providers

National Household Travel Survey

US Census
PMT and VMT from travel surveys and/or travel models

Average vehicle occupancy by trip purpose from household travel surveys and US Census Bureau

Vehicle occupancy counts

Transit ridership

Traffic and Heavy Vehicle Counts
Spreadsheet software

Travel demand model
PMT divided by VMT

Persons divided by vehicles

Average vehicle occupancy multiplied by vehicle volume
Regional travel demand models

Vehicle and person counts

Transit providers

National Household Travel Survey

US Census Bureau American Community Survey

MPO/RTPO Household Surveys