The Adams Motorcar had a 2 cycle engine directly coupled to the wheels. There was no clutch or reverse gear. To start it the crew pushed it and jumped on. To go in reverse the crew pushed from the opposite direction. There are many stories how the car got away without the driver. But the upside was that a crew could maintain more track a greater distance from the depot.
photos courtesy of the Robert collection http://www.rgusrail.com/