Connected Vehicles: Warnings for Hazards Not Immediately Visually Verifiable - NHTSA

Project summary:

Connected Vehicles systems will soon become important enabling technology for surface transportation; however, the scale, design, and functionality of these systems are still emerging and will impact their contribution to crash reductions for roadway users in the future. The purpose of these studies was to investigate the efficacy of different warning signals provided to drivers by Connected Vehicles technology to hazards in the environment that may be unseen by drivers. 

Overall, the series of studies demonstrated the efficacy of Connected Vehicles warning systems in improving driver safety. Future warning systems should alert drivers to imminent collision events once detected (even if not immediately verifiable by the driver) as close to 3.2 seconds TTC as possible. Forward collision warning systems which provide advanced alerts to drivers (i.e. 2.2 seconds TH) are beneficial in that they discourage drivers from encroaching on lead vehicles by only allowing them to follow closer the recommended 3 second TH safety distance. Drivers are less likely to accept such a distance; however, they may still experience a safety benefit if presented with a warning at 1.2 seconds TH. Finally, drivers should be presented with a feedback signal to indicate when a critical warning ceases to be a threat. Additional research on the relationship between prolonged exposure to similar warning systems and complacency (i.e. focusing on other in-vehicle, non-driving tasks) will allow for continued improvement in Connected Vehicle warning systems.