Close, but no cigar: assessment of a headway warning device

In the United Kingdom, drivers are advised to keep a two second gap between themselves and other vehicles even in optimal driving conditions. While drivers are not thought to have difficulty in detecting closure with a vehicle ahead, as long as the rate of change of the visual angle subtended by the lead vehicle is above threshold (greater than 0.003 radians per second), neither closure detection nor its rate of change easily allow a criterion of two seconds to be deduced and used. For the reasons discussed above, components such as distance and speed estimation, which would allow any such criterion to be deduced, are intrinsically unreliable. The study described sought to evaluate the effectiveness of a radar based warning system on the headway drivers chose to adopt while driving in real traffic. The author briefly describes the radar system used and the results of the trial