Driver Choices of Time-to-Collision Thresholds for a Collision Warning System

Collision warning systems (CWS) lower the risk of rear-end collisions by alerting drivers of imminent impacts (e.g., by sound). However, if warnings are perceived to be too far ahead of possible collisions, drivers may view them as annoying and gradually respond to them more slowly or even ignore them altogether. A possible solution is to let drivers set time-to-collision (TTC) thresholds themselves. This solution, however, to the best of our knowledge, has never been studied. Twenty six drivers used a smartphone-based CWS with an adjustable threshold on their daily trips. They were informed that they were allowed to change the warning threshold if they wished to do so. Their time-stamped acceleration and warnings were recorded. We aimed to test whether drivers who set the threshold comply more with warnings afterwards. We found that only three drivers changed the threshold and that the majority of drivers reported that they were content with the default threshold. In future studies we will examine whether the default TTC was indeed acceptable to most drivers or maybe it is the "power of default" that makes drivers refrain from customizing their CWS.