Passenger kilometers is a measurement used to quantify the distance traveled by passengers in a vehicle, such as a train, bus, or airplane. It is calculated by multiplying the number of passengers by the distance traveled. For example, if 100 passengers travel 200 kilometers, the total passenger kilometers would be 20,000. This metric is important for assessing the efficiency and usage of transportation systems. It helps in understanding travel patterns, planning services, and evaluating the environmental impact of different modes of transport. By analyzing passenger kilometers, authorities can make informed decisions to improve public transport and reduce congestion.