Effects of variable speed limit signs on the recall of fixed road signs

This field study was designed to investigate recall of signs on highways, especially recall of fixed danger warning signs on a highway with a variable speed limit system. Specifically, recall of a general warning sign with a supplemental sign 'traffic investigation' and a bicyclists warning sign located either 50 or 150 meters after the variable sign belonging was studied. As control, a highway with conventional fixed speed limits having no other signs in the vicinity was used. The data was collected by road side interviews. The main results showed that, on average, 6-28% of the drivers recalled the warning sign. The variable speed limit sign did not affect the recall of the fixed warning sign. Neither had the distance between the variable sign and the fixed sign an effect on the recall. A fixed speed limit sign was recalled much more likely (63-73%) than the warning signs. These findings suggest that the usage of fixed warning signs should be considered carefully to improve the detection of signs and thereby improve the effects on driver behaviour. It is recommended that the current signing policy should be reconsidered and perhaps rewritten, that is the number of the warning signs would be limited. For the covering abstract see ITRD E137489.