Abstract: A defective object such as a vehicle normally movable on a lane, assembly ne, or track is detected by a receiver on another object travelling behind the defective object, to avoid rear end collisions with the defective vehicle. For this purpose the vehicles are equipped with a signal receiver and with a signal damping member. The signal is transmitted in a transmission line extending along the lane, assembly line, or track. When a defect occurs, the damping member is moved into a position relative to the transmission line in which the damping member sufficiently dampens the signal so that the next following vehicle fails to receive the signal whereby a warning may be provided that the path ahead is not free or that it is blocked.