Design and Evaluation of Speed Limits for an Automated Section Speed Control System

In this study, a methodology for the selection of speed limits in sections enforced with automated section speed enforcement systems (ASSESs) has been proposed. Results of the speed control system have been assessed by speed monitoring after the system implementation in the Italian Motorway A3 Naples-Salerno. The speed limits were selected taking into account the average of the following values: (1) minimum design speed; (2) minimum speed consistent with the available stopping sight distance; and (3) operating speeds before the ASSES implementation. The first two criteria take into account safety whereas the third criterion takes into account the mobility needs. The speed limits selected with these criteria were then refined basing on: maximum difference between the section speed limit and the minimum speed evaluated with criteria 1 and 2, evaluation of critical conditions, and consistency between the speed limits and the highway function. Overall, non compliance to the speed limits was equal to 50%. Non compliance was higher for heavy vehicles (60-70%) than for light vehicles (32-65%). Non compliance of light vehicles was much higher in the sections with the most constrained alignments (64% in sections with speed limit equal to 80 kph vs. 34% in sections with speed limit equal to 100 kph). 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.