Empirical Analysis of Effects of Automated Section Speed Enforcement System on Traffic Flow at Freeway Bottlenecks

Because speed has been recognized as the most important contributory factor in fatal road crashes, speed management has been widely implemented in several countries to improve road safety. The automated section speed enforcement system is increasingly being used as an effective way to tackle speeding, especially on motorways and in tunnels. However, the effects on traffic flow patterns of such systems remain controversial. An empirical analysis of traffic flow patterns before and after the introduction of such a system along a freeway section with recurrent congestion is presented. Gathered data consisted of point measurements at detectors and average travel speeds of each vehicle crossing the stretch. The main observed features were (a) a strong homogenization of individual speeds and of mean speeds among the lanes, (b) a reduction in the strength of the bottleneck, (c) the emergence of significant oscillations in time of traffic characteristics, and (d) a sensible reduction of travel times during the congestion pattern caused by the bottleneck moving downstream of the section. Empirical evidence suggests that driver compliance with speed limits is the key factor in analysis of such speed management systems and that their concurrent application with dynamic speed limit strategies should be thoroughly evaluated with a particular focus on this measure.