Forward collision warning modality and content: a summary of human factors studies

Abstract

The report summarizes a nonexhaustive sample of 17 studies covering 27 experiments on human factors and forward-collision warnings. Subject samples ranged from 11 to 260 (median=30). Twenty-three experiments were conducted using driving simulators; 4 were on test tracks. Typically subjects followed a lead vehicle that braked abruptly, triggering audio, visual, tactile, or combined warnings. Response/reaction time was reported as a dependent measure in 18 of the 27 experiments, the number of crashes in 8, distance headway (gap) in 3, perceived urgency in 7 (both by the same authors), perceived annoyance in 11, and probability of warning recall in 1. Providing a warning leads to a more desired outcome. Response/reaction times were briefer in 9 of the 9 studies that considered this and all 4 of the studies that examined crashes reported fewer crashes with warnings. Warnings 4 to 10 dB above the background level led to the best performance, but only one study systematically varied warning intensity. Of the combinations explored, multimodal warnings tended to lead to better performance than unimodal warnings, though none of them considered seat-belt-pretensioner activation, an effective way to reduce crash injuries. Studies could be improved by the use of consistent crash scenarios, defined measures, predictions of performance, and including older drivers in test samples.