Passenger-miles is a measurement used to quantify the distance traveled by passengers in a vehicle, such as an airplane, train, or bus. It is calculated by multiplying the number of passengers by the distance they travel. For example, if 100 passengers travel 50 miles, that results in 5,000 passenger-miles. This metric is important for understanding transportation efficiency and usage. It helps transportation agencies and policy makers analyze travel patterns, assess the demand for services, and make informed decisions about infrastructure and resource allocation.