Abstract: A passive warning system for communicating vehicular deceleration and other information through a warning light. A microprocessor-based warning system according to the invention accounts for variations in vehicular speed in generating a warning signal having an intensity level and a blinking rate related to the rate of deceleration of the automobile, the ambient driving conditions and the speed of the automobile. The microprocessor is also programmed to measure speed variations more frequently as the speed of the vehicle increases, allowing information to be communicated in a timely manner. In one embodiment of the invention, the microprocessor is programmed to maintain the highest intensity warning signal activated for a predetermined period of time in order to inform other vehicles of an earlier speed reduction.