passengerkilometers

Passenger-kilometers, abbreviated PKM, is a unit of measurement used in transportation planning and policy to express the total distance traveled by passengers. One PKM corresponds to one passenger traveling one kilometer. PKM can describe activity for a single route, a mode, or an entire transportation system, and both the number of passengers and the distance traveled are taken into account.

Calculation: PKM is computed by multiplying the number of passengers by the distance of their trips and summing over all trips. For example, ten passengers traveling 5 km each contribute 50 PKM. Data sources include ticketing records, passenger surveys, and timetable or GPS data. PKM is commonly aggregated by mode (rail, bus, air, car) and by geography or time period.

Relation to other metrics: PKM is related to vehicle-kilometers (VKM), which counts the distance traveled by vehicles regardless of occupancy. Comparing PKM with VKM or with available seat-kilometers (ASK) allows assessment of occupancy and efficiency. In aviation, the load factor is PKM divided by ASK. PKM is widely used to measure demand, energy use, emissions intensity per passenger-kilometer, and transport system performance.

Limitations: PKM assumes equal weighting of passengers on a trip and may obscure distribution of distances among travelers. It also relies on accurate passenger counts and distance estimates, which can be challenging for multi-leg journeys and shared modes. Nevertheless, PKM remains a standard, comparable metric across modes and regions.