Abstract: Intelligent electronic circuit apparatus is disclosed for automatically controlling the hazard warning system (such as a tail light) of a motor vehicle so as to assist in preventing accidents. The apparatus includes a switch for selectively connecting the tail light with a voltage source and a control device for automatically closing the switch, thereby connecting the tail light to the voltage source, in response to a condition indicating a hazard to other vehicles in the vicinity. The invention provides means for sensing the driving environment of the motor vehicle and for changing the condition of response in dependence upon the sensed environment.