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Safety Impacts of Signing and Pavement Markings on Property-Damage-Only Crashes at Multi-Lane Roundabouts

Conventional intersections that have been replaced by multi-lane roundabouts have experienced a substantial reduction in both injury and fatal crashes. Property-damage-only (PDO) crashes have also been reduced at some of these roundabouts. However, some have experienced a significant increase in PDO crashes. This has caused some jurisdictions to question the suitability of multi-lane roundabouts despite their benefit of reduced injury and fatal crashes. The question arises as to why some U.S. multi-lane roundabouts have high numbers of PDO crashes whereas other outwardly similar roundabouts do not. This paper examines the hypothesis that the cause of the higher numbers of PDO crashes at some U.S. multi-lane roundabouts is driver confusion and information overload, arising from a combination of poor geometric layout, signing, and pavement markings. Successful roundabout design requires that the geometric layout, the signing, and the pavement markings act together to give a simple, clear message to the drivers, thereby avoiding driver confusion and reducing PDO crashes. This paper reviews research and explores the best practice for roundabout signing and pavement marking using established traffic engineering principles and discusses aspects of the 2009 Manual on Uniform Traffic Control Devices that may contradict these principles. The paper highlights two case studies of poorly performing U.S. multi-lane roundabouts, where the revised signing and pavement markings achieved 37–80% reduction in PDO accidents.