Curbing

On an open rural highway, changes in the roadway’s cross-section can be an effective means to help approaching drivers recognize the need to reduce their speed. Rural highways typically have no outside curbs with wide paved or gravel shoulders. Narrow shoulder widths and curbs on the outside edges of pavement, on the other hand, generally give drivers a sense they are entering a more urbanized setting, causing them to naturally slow down. Thus, consideration should be given to reducing shoulder widths and introducing curbs when installing a roundabout on an open rural highway.

Curbs help to improve delineation and to prevent “corner cutting,” which helps to ensure low speeds. In this way, curbs help to confine vehicles to the intended design path. The designer should carefully consider all likely design vehicles, including farm equipment, when setting curb locations. Little research has been performed to date regarding the length of curbing required in advance of a rural roundabout. In general, it may be desirable to extend the curbing from the approach for at least the length of the required deceleration distance to the roundabout.