Effects on speed and safety of point-to-point speed enforcement systems: Evaluation on the urban motorway A56 Tangenziale di Napoli Alfonso Montella *, Lella Liana Imbriani, Vittorio Marzano, Filomena Mauriello University of Naples Federico II, Department of Civil, Architectural and Environmental Engineering, Via Claudio 21, 80125 Naples, Italy ARTICLE INFO Article history: Received 11 August 2014 Received in revised form 27 November 2014 Accepted 28 November 2014 Available online 5 December 2014 Keywords: Highway safety Speeding Average speed enforcement Empirical Bayes method Crash modification factors Crash modification functions Safety performance functions ABSTRACT In this paper, we evaluated the effects on speed and safety of the point-to-point (P2P) speed enforcement system activated on the urban motorway A56 in Italy. The P2P speed enforcement is a relatively new approach to traffic law enforcement that involves the calculation of the average speed over a section. To evaluate the speed effects, we performed a before–after analysis of speed data investigating also effects on non-compliance to speed limits. To evaluate the safety effects, we carried out an empirical Bayes observational before-and-after study. The P2P system led to very positive effects on both speed and safety. As far as the effects on the section average travel speeds, the system yielded to a reduction in the mean speed, the 85th percentile speed, the standard deviation of speed, and the proportion of drivers exceeding the speed limits, exceeding the speed limits more than 10 km/h, and exceeding the speed limits more than 20 km/h. The best results were the decrease of the speed variability and the reduction of the excessive speeding behaviour. The decrease in the standard deviation of speed was 26% while the proportion of light and heavy vehicles exceeding the speed limits more than 20km/h was reduced respectively by 84 and 77%. As far as the safety effects, the P2P system yielded to a 32% reduction in the total crashes, with a lower 95% confidence limit of the estimate equal to 22%. The greatest crash reductions were in rainy weather (57%), on wet pavement (51%), on curves (49%), for single vehicle crashes (44%), and for injury crashes (37%). It is noteworthy that the system produced a statistically significant reduction of 21% in total crashes also in the part of the motorway where it was not activated, thus generating a significant spillover effect. The investigation of the effects of the P2P system on speed and safety over time allowed to develop crash modification functions where the relationship between crash modification factors and speed parameters (mean speed, 85th percentile speed, and standard deviation of speed) was expressed by a power function. Crash modification functions show that the effect of speed on safety is greater on curves and for injury crashes. Even though the study results show excellent outcomes, we must point out that the crash reduction effects decreased over time and speed, speed variability, and non-compliance to speed limits significantly increased over time. To maintain its effectiveness over time, P2P speed enforcement must be actively managed, i.e. constantly monitored and supported by appropriate sanctions. ã 2014 Elsevier Ltd. All rights reserved. 1. Introduction Drivers’ speed inconsistent with the road environment is among the most significant crash contributing factors (Council et al., 2010; Hauer, 2009; Montella and Imbriani, 2014; Montella et al., 2010, 2011; Neuman et al., 2009; OECD, 2006; Yannis et al., 2013). Speeding is both driving faster than the posted speed limit as well as driving too fast for the prevailing weather, light, traffic and road conditions, but within the speed limits (Montella et al., 2013; NHTSA, 2012). The relation between speed and safety rests on two pillars: (1) the relationship between speed and the crash risk and (2) the relationship between speed and the crash severity. Higher speeds imply greater driving task difficulty and therefore greater crash risk. At higher speeds, the time to react to changes in the environment is shorter, the stopping distance is larger, the manoeuvrability is reduced, and it is more difficult to react in time and prevent a crash. However, the greater effect of speed is on the injury consequences of the crashes. The higher the collision * Corresponding author. Tel.: +39 817683941; fax: +39 817683946. E-mail addresses: alfonso.montella@unina.it (A. Montella), lellaliana.imbriani@unina.it (L.L. Imbriani), vittorio.marzano@unina.it (V. Marzano) , filomena.mauriello@unina.it (F. Mauriello). http://dx.doi.org/10.1016/j.aap.2014.11.022 0001-4575/ ã 2014 Elsevier Ltd. All rights reserved. Accident Analysis and Prevention 75 (2015) 164–178 Contents lists available at ScienceDirect Accident Analysis and Prevention journal homepage: www.elsevier.com/locate/aap