Analysis of drivers’ compliance to speed limits enforced with an automated section speed enforcement system

This study evaluated the effectiveness of speed limits enforced with an automated section speed enforcement system (ASSES) through the analysis of compliance after the system implementation in the Italian Motorway A3 Naples-Salerno. The speed limits were selected taking into account take both the safety and the mobility needs. The system was activated on April 21, 2010 and the driving speeds were monitored in the two periods April 21, 2010 - May 11, 2010 and March 30, 2011 - April 20, 2011. Non compliance to the speed limits was higher for the heavy vehicles (w>3.5 tons) than for the light vehicles (w≤3.5 tons). This is very challenging because of the high severity of the crashes involving trucks, which is further increased by the higher speed. Non compliance of the light vehicles was much higher in the sections with the most constrained alignments (sections with speed limit 80 kph vs. sections with speed limit 100 kph, 65% vs. 40%). An explanation of this behaviour is that drivers do not adequately compensate for more demanding driving conditions by reducing speed if the safe speed is much lower than the speed desired in relation to the highway type and function. Overall, non compliance to the speed limits was 50.5% in 2010 and 57.4% in 2011. The decrease in the drivers’ compliance over time suggests that a weak enforcement strategy was applied. Higher compliance to the speed limits, according to the authors’ belief, might be achieved by a better strategy of communication and information to the road users and a speed limit management strategy synergic between the highway agency and the Police who actually manages the commitments of fines.