Abstract: A rail vehicle of a type for running on a pair of parallel rails has an apparatus for detecting the distance between it and a forward remote vehicle, for detecting the speed of the forward remote vehicle and for detecting discontinuities in the track. This is achieved by a first electrical contact for engaging one of the rails which applies a voltage between the contact and the first set of wheels of the vehicle which generate a short across the two rails. The spacing between the contact and the first set of wheels is such that a current runs from the contact forwardly of the vehicle to a short circuit across the rails generated by the next adjacent remote vehicle and back to a second electrical contact on the vehicle contacting the other rail. The magnitude of the voltage difference between the second contact and the first set of wheels is then measured to provide an indication of the distance between the vehicle and the next adjacent remote vehicle.