Time-to-collision judgments under realistic driving conditions.

Objective: This study examined perceived time to collision (TTC) with automobile drivers under realistic approach, rear-end crash scenario conditions.

Background: TTC refers to the time before impact if prevailing conditions continue.

Method: In this test track study involving 51 drivers ranging from 20 to 70 years old, the driver's vision was occluded at either 3.6 or 5.6 s TTC during an in-lane approach to a lead vehicle. Drivers provided TTC estimates by pressing a button the instant they felt that they would have collided with the vehicle ahead.

Results: Results indicated that TTC was consistently underestimated. The TTC ratio (perceived TTC/actual TTC) increased as driver speed decreased and as relative speed increased. These ratios were largely unaffected by age, gender, actual TTC, viewing time (1 s vs. continuous), and the presence of an eyes-forward, mental addition distraction task.

Conclusion: Overall, these results suggest that under these low TTC conditions drivers estimate TTC in a relatively uniform fashion and that they are capable of providing this estimate based on a brief glimpse to the vehicle ahead.

Application: These results are being used to develop an alert timing approach for a forward collision warning system intended to assist drivers in avoiding rear-end crashes with the vehicle ahead.