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