Comparison of driver's reaction time associated with driving speed on actual driving

It can be said that a collision happens when a car's stopping distance is longer than the car's headway distance. The stopping distance is some times prolonged unexpectedly. The stopping distance of the car comprises the braking distance and the reaction distance. One of the causes of the unexpected prolongation of the stopping distance is a lengthening of the reaction distance. The reaction time is the distance a vehicle travels from the time of the first appearance of an obstacle or a sudden change in the surroundings to the time when the brake system works. The authors measured the driver's reaction times (RTs) at the speed of 0km/h, 20km/h, 40km/h and 60km/h. The result of the experiment showed that the mean RTs for driving conditions were larger than that of a stopping condition. There are no differences between the mean RT of each speed condition. But there are differences between the standard deviation (SD) of RT. The result of other experiments showed that the RT while driving under hasty conditions was larger than that while driving under ordinary condition. Thus, the authors suggested that hasty driving must be deterred to avoid collisions.