Comparison between younger and older drivers of the effect of obstacle direction on the minimum obstacle distance to brake and avoid a motor vehicle accident.

Our objectives were to determine the effects of age and direction of appearance of an obstacle on the minimum obstacle distance to brake and avoid a motor vehicle accident. Ten younger and 10 older drivers were tested in a custom-made driving simulator using an animation of a straight suburban road. Driving at 50 km/h, participants suddenly encountered pedestrians appearing at increasingly closer distances in front, from the left or from the right. They then had to brake as fast as possible and come to a complete stop before running over the pedestrian. Results showed that older drivers had 1.8m greater minimum obstacle distance than younger drivers. This decreased ability with age appeared to be due to a decline in response initiation. Pedestrians appearing from the periphery also resulted in 2.1m (left) and 2.8m (right) greater minimum obstacle distance than those appearing directly in front. This decreased ability with obstacle direction appeared to be mostly due to declines in response initiation and response geometry. Finally, the difference with age was greater when pedestrians appeared from the right compared to the left or front. Therefore, it is important to include both temporal and geometrical performance measures in studies on motor vehicle accidents.