Do curb extensions reduce speeds?
A single traffic calming treatment may be inadequate to reduce speeds, especially if education and enforcement are absent from the mix. It's the cumulative effect of a host of traffic calming techniques that makes a difference. Key ingredients are on-street parking, narrow lanes, curb extensions, vertical elements (such as trees) and buildings close to the street.
Example curb extension in Madison, Wisconsin.
Photo: Dan Burden.
Curb extensions are primarily a pedestrian safety measure rather than a speed deterrent measure. No known studies have proven that curb extensions alone reduce speeds. Curb extensions at intersections usually improve pedestrian visibility: the first part of a crossing when a pedestrian enters the roadway is the riskiest. Curb extensions slow motorists at a point of conflict by tightening the turning radius, which improves motorist right-of-way compliance. Anecdotally, practitioners report slower speeds and say that right-turning vehicles are more likely to slow down.
More importantly, curb extensions shorten the street crossing distance for pedestrians thereby reducing their exposure to motor vehicles. On arterial and collector roads, complaints about speeding are often complaints about pedestrian safety; curb extensions are one way to address this issue.
Additional considerations include mountable, vertical or barrier curbs.