Abstract
Experiments on estimating TTC values show that TTC is consistently underestimated. To evaluate driver use of TTC when actually taking evasive action, a field experiment was conducted where subjects approaching a stationary object were instructed to start braking at the latest moment they thought they could stop in front of the object. The results reveal that TTC at the onset of braking increases with speed, but less than could be expected from a constant deceleration model.