Curb Extension - Design, Advantages and Disadvantages

Design, Advantages and Disadvantages

The Pedestrian and Bicycle Information Center advises that curb extensions ought not encroach on travel lanes, bicycle lanes, or shoulders, and should not extend more than 1.8 m (6 ft) from the curb. Some curb extensions are built with the bike lane passing through (making the extension an island, separated from the main sidewalk by a narrow bike lane).

One study has found that pedestrians crossing at curb extensions have to wait for fewer vehicles to pass before a motorist yields to allow them to cross. The study was too small to determine whether other measures of effectiveness, such as percent of pedestrians crossing after a motorist yields, were significant.

Poorly designed curb extensions can pose a hazard to cyclists, as they force cyclists from their position at the road side (or in a roadside bike lane) into the narrowed gap. They can also damage vehicles if the curbs extend too close to traffic lanes.

Curb extensions have not been found to affect the speed of vehicle traffic.

Author Randal O'Toole argues that curb extensions are used to increase traffic congestion to discourage the use of automobiles by reducing the number of lanes available for automobiles. In particular, curb extensions can be used to block turn lanes, forcing turning vehicles to remain with the forward moving traffic. Curb extensions do prevent drivers from using parking lanes or shoulders as right turn lanes.

However, reducing the crossing distance also reduces the time needed to cross the street. This allows a reduction in the length of the pedestrian phase at signalized intersection, and reduces the time needed to yield to pedestrians at stop sign controlled intersections. This at least partially compensated for any loss in vehicle capacity.

Curb extensions complicate drainage. They obstruct the gutter, so a catch basin is needed at the uphill end to keep a puddle from forming. An alternate solution is placing a gap in the curb, allowing the stormwater in the gutter to irrigate a rain garden in the curb extension.

To facilitate street sweeping, the internal and external curvatures of the extended curb section are moderately graduated.

Retroactively adding curb extensions to older, established communities has been controversial in some instances, due to the installation of the extensions reducing the availability of on-street parking for some properties, particularly in cases where the curb extension has been installed on its own and not in conjunction with a crosswalk.