There is described a deceleration warning system for installation in a road vehicle. The deceleration warning system emits a rearwardly-directed warning light in response to a sensed deceleration of the vehicle. The deceleration warning system can also emit a warning light when the vehicle braking system is operated above a predetermined operating level. Also described is a collision warning system for a vehicle wherein a warning light is emitted in response to the rate of change of distance between the vehicle and another object, when the rate of change of distance is above a predetermined level.
