Drivers' immediate responses to traffic signs

Abstract

Earlier studies have shown that when stopped on the road and requested to report a traffic sign which they just passed, drivers are able to do it correctly more often if the sign is of significance to them. Thus, such a sign is either better detected or better remembered than the less significant ones. In this study, speed changes of 2185 drivers were unobtrusively measured on a steeply rising right-hand bend of a minor road where an experimental sign suddenly came into view. Three signs were randomly alternated, with and without a specific warning flasher: Danger, Children and Speed Limit 30 km/h. It was found that the speed decrement was dependent on the significance of the stimulus sign: the more significant the sign the greater the drivers' immediate response to it. The analysis of speed-change distributions revealed that drivers detected each sign equally well and responded to each by releasing the accelerator, but they responded more strongly to the more significant signs. In the light of these results, earlier findings indicate that significant signs are better remembered by drivers when stopped and interviewed.

This study, once again, supports the explanation that the problems of the traffic-sign system are mainly due to motivational factors. However, these results also showed perceptual limits in using signs for traffic control: a substantial effect which a specific warning flasher had on the drivers' responses in cloudy and rainy weather and in the dark disappeared in sunny weather indicating that the flasher was not detected against a bright sky.