On the impact of average speed enforcement systems in reducing highway accidents: evidence from the Italian Safety Tutor

At the end of 2005, Autostrade per l’Italia (ASPI) and the Italian traffic police progressively deployed along the Italian tolled motorway network an average speed enforcement system, named Safety Tutor, able to determine the average speed of vehicles over a long section to encourage drivers to comply with speed limits and improve safety. The aim of this study was to empirically test the extent to which Safety Tutor led to a reduction in both total and fatal accidents on Italian highways during the period of 2001–2017. To do so, we carried out a generalized difference-in-differences estimation using a unique panel dataset that exploits the heterogeneous accident data within all tolled motorway sectors in a quasi-experimental setting. To deal with the potential endogeneity of the non-random placement of Safety Tutor sites, we utilized an instrumental variable strategy by using the network of motorway sectors managed by ASPI and its controlled concessionaires from 2005 onwards (i.e., when the technology was available) as an instrument to predict Safety Tutor adoption. We found that a 10% increase in Safety Tutor coverage led to an average reduction in total accidents of 3.9%, whereas there is no evidence of a significant causal effect of Safety Tutor in reducing fatal accidents.