Narrow shoulders


Loenis, B.; Schermers, G.; Petegem, J.W.H. van



A road shoulder is that section of roadway immediately adjacent to the travel lane. The shoulder can be surfaced or unsurfaced. The lack of adequate shoulder width has been identified as a risk factor in studies on two-lane rural highways. Paved shoulders may increase safety by providing a recovery area for drivers who have left the travel lane and they provide a place for a driver to stop a defective vehicle and avoid crashes. However, at the same time, shoulders may to some extent increase the risk of conflicts caused by vehicles stopped on shoulder and by inadvertently inviting higher speeds (wide shoulders and wide lanes lead to a generous cross section). The described effects depend not only on the presence of a road shoulder but also on the width of the road shoulder. A wider road shoulder provides the driver with more recovery area but may trigger higher speeds. Five USA studies on shoulder width were coded. All five studies showed that wider shoulders were associated with a decrease in crashes. One study also combined the variables shoulder width and the presence of shoulder rumble strips, and showed a decrease of the number of crashes. Another study combined the variables shoulder width and speed limit, and showed a decrease of crashes for an increase of the shoulder width on roads with a higher speed limit. A third study combined the variables shoulder width and lane width and showed a decrease in the number of crashes. The remaining two studies showed the single effect of shoulder width on the number of crashes. In general, the evidence is conclusive that narrow shoulders increase the number of crashes compared to wider shoulders, be it for different conditions.

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European Road Safety Decision Support System, developed by the H2020 project SafetyCube



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European Commission, Brussels