A rail replacement bus service uses buses to replace a passenger train service on a temporary or permanent basis. The train service that is replaced may be of any type such as light rail, tram, streetcar, commuter rail, regional rail or heavy rail, intercity passenger service. The rail service may be replaced if the line is closed because of rail maintenance, a breakdown of a train, a rail accident or a strike action or to simply provide additional capacity or if the rail service is deemed not economically viable.
Terms for a rail replacement bus service include bustitution (a portmanteau of the words "bus" and "substitution", or bustitute)[1] and bus bridge.[2] Substitution of rail services by buses can be unpopular and subject to criticism and so the term bustitution is often used pejoratively.[3][4]