A wide variety of metrics exist to help planners evaluate the performance of transit, and different metrics are appropriate for different circumstances and types of agencies. Generally, transit metrics can be divided into "supply-side" metrics (i.e., that evaluate how much and what kind of service is being provided), and "demand-side" metrics (i.e., that evaluate how many people are using the service, and in what ways).
Supply-Side Transit Metrics
Vehicle Revenue Miles are the total number of miles traveled by a vehicle in revenue service, i.e., a vehicle that is open to ridership by the general public.
Vehicle Revenue Hours are the total number of hours during which a transit vehicle is operating in revenue service. VRH is frequently seen as a preferable supply-side metric to VRM, because it is less influenced by the relative sprawl or density of an agency's service area.
Demand-Side Transit Metrics
Ridership is the most straightforward, consistent, and regularly measured metric that can be used to assess the performance of transit in California on various geographic scales. The 2018 STSP Recommendations Report recommends that California adopt a statewide performance target of doubling transit boardings per capita in the state between 2015 and 2030.
Various ways exist to measure and quantify ridership. They include:
Unlinked Passenger Trips. This counts "the number of times passengers board public transportation vehicles. Passengers are counted each time they board vehicles no matter how many vehicles they use to travel from their origin to their destination and regardless of whether they pay a fare, use a pass or transfer, ride for free, or pay in some other way." Unlinked passenger trips are also called "Boardings."
Linked Passenger Trips counts the number of end-to-end trips made on a transit network. A trip that requires a transfer from one bus line to one rail line, for example, would count as two unlinked trips but one linked trip.
Passenger Miles counts the cumulative number of miles travelled by all transit passengers. One passenger traveling one mile counts as one PM, as do two transit passengers traveling one-half mile each.
Passenger Hours counts the cumulative amount of time that passengers spend riding transit. One passenger riding transit for one hour counts as one PH, as do two passengers traveling for 30 minutes each.