In-depth Investigation of Run-off-the-Road Crashes on the Motorway Naples-Candela

In the paper, results from in-depth investigation of 1,092 run off the road (ROR) crashes on the motorway A16 (Italy) are presented. The research is aimed at pointing out risk factors that can address highway agencies and designers toward the selection of safety countermeasures aimed at reducing ROR crashes frequency and severity. Crash data were collected trough the analysis of police crash reports and relate to the period 2001-2005. Basing on police and hospital reports, each crash was categorized in six injury levels. To determine whether a specific crash pattern of the analysis group was significantly different from that of the control group, the Chi Squared (χ2) test with Yates’ correction was performed. Severity of motorcycle crashes was significantly higher than severity of other vehicle types. In adverse environmental conditions (night time and wet pavement), crash severity was lower than in favourable conditions. Crashes against ditches, walls, foreslopes, and backslopes were more severe than crashes against roadside steel safety barriers. Comparison between severity of crashes against longitudinal safety barriers and their blunt end terminals showed a dramatic increase in crash severity against the terminals. Thrie-beam roadside barriers that meet EN 1317 performance criteria showed a smaller crash severity and a better performance compared to older W-beam roadside barriers. Median New Jersey concrete barriers, compared to median steel safety barriers, showed greater crash severity and greater proportion of rollovers, not counterbalanced by a significant better behaviour in relation to penetration and override.