Abstract: A rail system of the type in which a vehicle runs along a track to carry articles such as goods from one location in an industrial plant or other installation, to another location. At some point along the path an arm is provided for engagement with the vehicle and is swung with an angular velocity determined by the vehicle speed. A centrifugal clutch, effective when the angular velocity exceeds a predetermined level equivalent, say, to the maximum safe speed for the vehicle, can operate a cam to control a spring-loaded stop for the vehicle or car so that the stop can be rendered effective to bring the vehicle to standstill when the sensor detects the excessive speed.