Advanced Audio-Visual Multimodal Warnings for Drivers: Effect of Specificity and Lead Time on Effectiveness

Multimodal warning systems have been proved to be more effective than traditional unimodal driving warning systems, but few previous studies have systematically discussed the factors affecting the effectiveness of multimodal warnings. This study was designed to investigate the influence of the specificity of warning content and warning lead time on the effectiveness of audio-visual multimodal warning system based on indicators of drivers' behavior performance and subjective evaluation. We conducted the experiment in a driving simulator with 37 participants, which included 8 common dangerous driving scenarios, with visual warnings provided via head-up display and accompanied by audio warnings provided via two speakers in front of the participants. Results showed that by using the combination of specific visual and general auditory warning content, drivers can obtain a fast braking response, remarkable TTC at the braking onset, and a low likelihood of collision, which can improve driving safety. Although drivers obtain a fast braking response with a late warning (lead time of 2.5 s) in audio-visual warning system, they feel excessive workload and insufficient understandability of warning content compared with those with an early warning (lead time of 4.5 s).