 Airplanes operate with headways measured in hours or days, freight trains and commuter rail systems might have headways measured in parts of an hour, metro and light rail systems operate with headways on the order of 90 seconds to 5 minutes, and vehicles on a freeway can have as little as 2 seconds headway between them.Headway is a key input in calculating the overall route capacity of any transit system.A system that requires large headways has more empty space than passenger capacity, which lowers the total number of passengers or cargo quantity being transported for a given length of line (railroad or highway, for instance).