Mauro D'Apuzzo

Safety evaluation of automated section speed enforcement system

Because speeding is one of the most significant contributing factors to fatal crashes, most road agencies attempt to achieve the right operating speed by imposing speed limits. Speed limit violations are prevalent, even on motorways with speed cameras. A problem with speed camera enforcement is that some motorists brake before passing a camera location and then exceed the speed limit after passing. This sudden braking can cause dangerous situations, crashes, and traffic jams. Furthermore, safe operating speed is not achieved where there are no cameras, especially where enforcement is overt, as in Italy. A new technique to overcome these problems is an automated section speed enforcement system, Safety Tutor. Unlike conventional speed meters, which measure vehicle speed at one point, the new technique determines average speed over a long distance. This study evaluated the safety effectiveness of the Safety Tutor system installed on Italian Motorway A1 Milan–Naples in 2007. An empirical Bayes observational before-and-after study was performed. The estimate of the total crash reduction is 31.2%, with a lower 95% confidence limit of 24.3%. The greatest crash reductions were observed for severe crashes and crashes at curves. Reduction was 55.6% for severe crashes, 26.6% for nonsevere crashes, 43.4% at curves, and 28.4% at tangents. However, the systems effectiveness decreased over time. The crash reduction was 39.4% in the first semester after the systems activation and 18.7% in the fifth semester after activation. Results strongly support activation of the new automated system owing to highly significant and substantial safety effects. The decrease in system effectiveness over time may be correctible with higher levels of enforcement.

A New Methodology for Stochastic Modelling of Pay Factors in Hot-Mix Asphalt Pavements

ABSTRACT Since 1990 several research projects developing any Pay-Adjustment (PA) procedure for implementing Performance Related Specification (PRS) in Hot-Mix Asphalt (HMA) pavement construction have been issued. Previous studies proved that an approach based on life-cycle cost analysis and Monte Carlo simulation was an effective way to develop rational pay-adjustment procedures. However, the PRS systems developed so far had some significant weaknesses in the modelling of the variability of Materials and Construction (M&C) characteristics with corresponding PA. Furthermore they are mainly based on an empirical approach rather than on a mechanistic one. A new approach to model M&C variability in PRS systems, based on beta distribution, is introduced and a new stochastic method for pay-adjustment evaluation is developed. These criteria were embedded in a mechanistic system framework based on life-cycle cost analysis and Monte Carlo simulation. The model has been recently applied to a real case study and results are reported and analysed in this paperwork.