How to drive drivers nuts effect of auditory, vibrotactile, and multimodal warnings on perceived urgency, annoyance, and acceptability

With semiautonomous vehicles and innovative assistance systems flooding the market, the characteristics of warning signals for automotive human-machine interfaces determine their effectiveness and usage. Within the context of advanced driver assistance systems, poorly designed warning signals have the potential to startle and distract drivers. Previous studies have investigated the effectiveness of multimodal warning signals and found that such signals reduce braking times. They are also associated with high levels of perceived urgency. This study aimed to investigate the effects of auditory, vibrotactile, and multimodal warning signals on perceived urgency, annoyance, and acceptability while varying the level of participants' mental workload and the characteristics of the warning signals (interpulse interval). Results show that, compared with other signal modalities, multimodal warning signals appear to be effective in low-workload conditions but such effect disappears as the overall level of workload increases. These results are useful for the development of an adaptive warning signal system.