A rail replacement bus service replaces 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 inter-city passenger service. The railway 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; It may simply provide additional capacity or if the railway service is deemed not economically viable.