Report numberRA-2013-004
TitleIdentifying crash patterns on roundabouts: an exploratory study
AuthorsEvelien Polders
Stijn Daniels
Winfried Casters
Tom Brijs
Published byPolicy Research Centre for Traffic Safety 2012-2015
Number of pages36
Document languageEnglish
Partner(s)Universiteit Hasselt
Work packageWP2: Risk analysis

Objectives: Roundabouts are a type of circular intersection control generally associated with a favourable influence on traffic safety. International studies of intersections converted to roundabouts indicate a strong reduction in injury crashes, particularly for crashes with fatal or serious injuries. Nevertheless, some crashes still occur at roundabouts. The present study aims to improve the understanding of roundabout safety by identifying crash types, locations and factors that are associated with roundabout crashes.


Methods: An analysis of 399 crashes on 28 roundabouts in Flanders-Belgium was carried out based on detailed crash descriptions, i.e. crash data and collision diagrams. The crashes are sampled from police-reported crashes at roundabouts in the region of Flanders, Belgium. Collision diagrams of the registered crashes were used to distinguish 8 different crash types. The roundabout itself is divided into 11 detailed and different typical segments, according to previously established knowledge on the occurrence of crashes at roundabouts. This procedure allows to include the detailed crash location for systematic analysis. The exact crash location of each crash is determined by using the location information in the collision diagrams to assign every crash to the corresponding segment. The 8 roundabout crash types are examined by injury severity, crash location within the roundabout, external factors (weather/ light conditions) type of roundabout (single-lane, double-lane), type of cycle facility (mixed, cycle lanes within the roundabout, separate cycle paths and grade-separated cycle paths) and type of involved road user.


Results: Four dominant crash types are identified: rear-end crashes, collisions with vulnerable road users, entering-circulating crashes and single-vehicle collisions with the central island. Crashes with vulnerable road users and collisions with the central island are characterised by significantly higher proportions of injury crashes. About 80% of the crashes occurred on the entry lanes and the circulatory road (segment 1-4 and 6). Specific crash types at double-lane roundabouts are collisions with the central island and sideswipe crashes. Road users that are the most at risk to be involved in serious injury crashes at roundabouts are cyclists, motorcycles, mopeds and pedestrians.


Recommendations: To reduce the number of crashes with vulnerable road users, it is desirable that future roundabouts are constructed without integrated cycle lanes. Severe single-vehicle collisions with the central island can be reduced by securing the visibility of the central island. Since, the majority of these crashes take place at night it is important that the roundabout and central island are well-illuminated. From the safety point of view, it is also crucial that roundabouts are constructed in such a way that the speeds of the approaching road users are reduced.

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The Policy Research Centre for Traffic Safety carries out policy relevant scientific research under the authority of the Flemish Government. The Centre is the result of a

cooperation between Hasselt University, KU Leuven and VITO, the Flemish Institute for Technological Research.


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