Looming Auditory and Vibrotactile Collision Warnings for Safe Driving

Looming auditory warning signals (that is, signals whose intensity increases over time) have proven to be particularly effective in terms of reducing a driver’s brake reaction times (BRTs) to impending collisions, and are also associated with very low false alarm rates. We report two experiments designed to further investigate how the presentation of looming auditory warnings with increasing frequency or increasing spatial extent would compare to those with increasing intensity. A third experiment was conducted in order to evaluate the potential efficacy of presenting looming warnings to drivers in another modality, namely via vibrotactile signals. Participants’ speeded BRTs to potential collision events following the presentation of various warning signals in a simulated car following scenario were measured. While both looming frequency and spatial warnings were effective in terms of speeding the driver’s responses to critical driving events, the magnitude of the benefit resembled that of a typical nonlooming constant intensity warning. Looming intensity warnings outperformed their looming frequency counterparts in terms of facilitating drivers’ collision avoidance responses. As for vibrotactile warnings, the results revealed that looming vibrotactile stimuli did not offer any additional benefits over and above the other non-looming vibrations tested in the study. The implications of these findings for collision warning systems design are discussed.