Three studies evaluated the potential risks and benefits of an advance brake warning system . The system is based on a sensor attached to the accelerator that sends a signal to the brake light whenever the accelerator is released in a sudden manner (0.3 m/s - typical of emergency braking). The signal turns the brake lights on for 1.0 second. If during that time the driver actually brakes, then the following driver perceives a continuous brake light that comes on approximately 0.2 s before the brakes are actually applied (equivalent to the time it takes to move the foot from the accelerator pedal to the brake pedal). If the driver does not brake, then the brake light goes off within 1.0 s (essentially signalling a false alarm). The first study, a field study, showed that the ABWS has a false alarm rate of 25% and that, in general such emergency braking actions are relatively rare. The second study evaluated the additional time that would be provided to the following driver when the brake lights of the car ahead are activated by the ABWS. In a laboratory study, subjects braked in a simulator in response to the onset of the brake lights of the car ahead. The results showed that the critical movement time from the accelerator to the brake pedal (i.e., the added time that a following driver would have to respond) is approximately 0.2 s, and it is not greatly influenced by the level of expectancy. The third study was a computer-based Monte Carlo simulation that evaluated the likelihood of crash prevention due to ABWS under different conditions of speed, road conditions, and headway distances. The results showed that the ABWS should be very effective whenever the headway is under 1.5 seconds. This was true especially under dry road conditions, and regardless of the driving speed. The final study was a fleet study with nearly 400 matched pairs of vehicles - with and without the ABWS - that were tracked for an average of 3 years. The fleet study failed to find a statistically significant benefit of the ABWS. In conclusion, while the ABWS does not compromise safety, its benefits in real world driving are sufficiently small that its incorporation into the vehicle brake-communication system is questionable.