A transit injury is physical damage or harm to any person requiring medical treatment, which occurs under the collision, derailment, personal casualty, fire, or bus going off the road categories of NTD reporting. For transit employees, an injury includes an incident that results in loss of time from duty. The denominator for this measure is passenger miles. A separate Source and Accuracy Statement has been prepare for passenger miles. Passenger miles exclude travel to and from storage facilities, training operations, road tests and deadhead travel, as well as school bus and charter service.
Passenger miles are the cumulative sum of the distances ridden on passenger trips.
Transit authorities have accurate counts of unlinked passenger trips and fares. An unlinked trip is recorded each time a passenger boards a transit vehicle, even though the rider may be on the same journey. Transit authorities do not routinely record trip length. To calculate passenger miles, total unlinked trips are multiplied by average trip length. To obtain an average trip length for their bus routes and rail routes, transit authorities use a FTA approved sampling technique.