Traffic safety effects of advanced warning flashing lights at intersections on high-speed roads, Perth metropolitan area

A study was undertaken to evaluate effects of Advanced Warning Flashing Lights (AWFLs) at a sample of 25 intersections on Perth metropolitan highways having open road section speed limits ranging from 70 to 100 km/h. The lights had been installed over the period between 1993 and 2000. The study methodology was based on a “before/after” design by comparing the crash frequency and costs of crashes before and after installation of the AWFLs, over equal length time periods. The estimates of the effects were based on the crash data collected over 62.94 years of operations at the sample of intersections.

The study showed that there was a reduction of 5 fatal crashes after the installation of the lights at the affected 400 m approach road sections including the intersections. The AWFLs were found to be associated with significant change in types of crashes such that more severe crashes were reduced and less severe crashes increased. The expected changes were as follows: 22% reduction in right turn against crashes, 17% reduction in right angle crashes, 12% increase in rear end crashes, 11% reduction in side-swipe crashes, and 14% increase in other types of crashes. The overall increase in all types of crashes was estimated at 3%, well below expected of 6%. A multivariate analysis indicated that the “after” period is characterised by: fewer fatal crashes, fewer right turn against and right angle crashes, more rear end crashes, more crashes on 100 km/h roads than on <=90 km/h roads, and more crashes at road sections than at intersections.

Estimates of effects of AWFLs in terms of cost of crashes suggested that the reduction in the costs was in the range between $14,000 and $139,000 per intersection per annum. It is estimated that AWFLs may reduce cost of crashes by up to 22%. It was estimated that AWFLs were at least three times more effective in reducing cost of crashes involving heavy vehicles than the cost of crashes involving other types of vehicles.