Safety Effects of Height of Central Islands, Sight Distances, Markings and Signage at Single-lane Roundabouts

Søren U. Jensen, Paper from 5th International Symposium on Highway Geometric Design, June 2015

The height of central islands, sight distances, pavement markings and signage seem to have some influence on safety at single-lane roundabouts. The paper presents new information based upon a before-after safety study of converting intersections to 265 single-lane roundabouts in Denmark. Results from previous studies on these topics are included in the paper for comparison and discussion.

Non-transparent central islands higher than 1.9 meters produce better safety effects compared to lower central islands at single-lane roundabouts. A consequence of high central islands is fewer accidents between entering and circulating vehicles.

Certain approach sight distances may worsen safety at urban single-lane roundabouts. If upstream and circulating approach sight is given to approaching road users about 17-40 meters before the yield line then safety is not good.

If there is a truck apron around the central island then marking an edge line between the truck apron and the circulation seems to improve safety particularly at urban single-lane roundabouts. A two meters wide truck apron seems to be safest. Yield ahead signs and markings, roundabout plagues, destination signs and rumble strips all prior to the entry of single-lane roundabouts seem to improve safety considerably.



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