A speed reduction warning system that senses vehicle deceleration rate and upon reaching preset limits flashes an illumination device at different rates signaling the operator following the vehicle to the rate of deceleration. The system generally includes a processing unit, an input to the processor that senses deceleration or acceleration rate from the odometer of the vehicle, and an output illumination device. The illumination device includes an indicator that flashes at varying rates controlled by the processor. The processor includes storage having a plurality of ranges stored that are the deceleration rates that the system responds to. In application, with the vehicle in motion, the deceleration or acceleration rate of the vehicle is detected by the input device and supplied to the processor. A value is calculated by the processor representing whether the vehicle is decelerating and if so, the rate of deceleration. If the value is within one of the ranges in storage, the processor sends a corresponding output signal to the illumination device. Once the vehicle is stopped or begins to accelerate the output signal is extinguished by the processor, automatically. The system can further include means such that the indicator of the illumination device activates a selected illumination when the vehicle's anti-lock brake system is applied, or a steady illumination when the vehicle's speed is below 5 mph.