Personkilometre

Person-kilometre (PKM) is a unit of travel that measures the movement of people rather than vehicles. It is defined as the travel of one person for one kilometer. The calculation is PKM = number of persons × distance traveled (in kilometers). For example, three people traveling 4 kilometers each produce 12 PKM.

PKM is used to aggregate travel demand across modes and to normalize energy use and emissions. It provides a way to compare the efficiency and impact of different transportation options on a per-person basis. In statistics and policy analysis, PKM is often expressed alongside energy intensity or emissions, such as grams of CO2 per PKM or megajoules per PKM. Higher vehicle occupancy lowers energy and emissions per PKM, even if total distance traveled remains the same, making PKM a useful metric for assessing efficiency improvements and modal shifts.

Applications include transport planning, performance benchmarking, and emissions accounting. PKM helps researchers and planners evaluate mode shares, forecast demand, and set targets for reducing environmental impact. It is also used in accessibility and urban mobility studies to reflect the amount of travel experienced by people rather than by vehicles.

Limitations include its equal treatment of all persons, disregarding trip purpose, duration, or comfort. PKM does not cover freight or goods transport, and it relies on accurate occupancy data. It also does not distinguish short versus long trips, which can influence policy implications and planning outcomes.