Drivers' estimates of time to collision.
Drivers' estimates of time to collision were determined in a laboratory simulation using film segments made from a following vehicle approaching a lead vehicle, which was also in motion. Headway, approach speed, and viewing time were varied to make a total of 48 conditions. It was found that, provided the angular velocity subtended by the lead vehicle was above a threshold value of about .003 radians/sec, the driver was able to give reasonable estimates of time to collision. The standard deviation of the estimates varied linearly with the time to collision. Although drivers underestimated the time to collision when it was small, the large standard deviation shows the possibility of rear-end collisions due to poor estimation of time to collision, especially when the times for control action and vehicle deceleration are considered.