Intersections constitute only a small part of the overall highway system,yet intersection crashes constitute a significant portion of the total crashes. In order to reduce crashes and increase capacity, recently many intersections have been converted into roundabouts. Despite the good safety record, roundabout performances can be degraded if precautions are not taken. Therefore, information on the safety of roundabouts is helpful in identifying existing deficiencies and in refining the design criteria currentlybeing used. Aim of the paper was to investigate crash contributory factors in 15 urban roundabouts located in Italy. Crash data refer to the period2003-2008. At each roundabout, a diagnosis aimed at identifying crash contributory factors was performed. Two different level of confidence of contributory factors were used: major contributory factors and minor contributory factors. For each roundabout, crash data were summarized using collision diagrams and map diagrams containing all relevant geometric data. Each roundabout was inspected by a team of safety specialists once every year from 2004 to 2009, both in daytime and in night time. For each crash, the original crash report form, the collision diagram, the map diagram, the checklists, and the site inspections supported the identification of the contributory factors. In most crashes, a combination of contributory factors was identified. The contributory factors were classified in the following categories: road user, vehicle, geometric design, markings, signs, road environment, and pavement. The most frequent contributory factor was geometric design. In almost 60% of the total crashes at least one geometric design factor was found. In many crashes, road users’ wrong behavior was significantly affected by a combination of roundabout geometric design, markingsand signs which gave wrong cues.
Abstract