Bump-outs (also known as “curb extensions“) have become commonplace in many subdivisions across the country. They are also common in the existing neighborhoods as a means of traffic-calming. The purpose is to provide an additional element in protecting the vehicles parked on the street and enabling shorter, safer crossing for the pedestrian at the intersection. The bump-out can be a costly add-on for a neighborhood considering the additional curb that is involved and additional measures that need to be taken to handle stormwater. Careful consideration should be given whether a bump-out is most appropriate per the situation. In the instances where bump-outs are desired, I have developed a few variations of the bump-out that can effectively manage stormwater with infiltration, calm traffic and ease the costs of additional curbing.
The graphic to the right illustrates a narrow street cross-section for two-way traffic measuring 20-feet to 22-feet in width from curb to curb. Adjacent to the rolled curbs (gradually sloped curbs that permit vehicles mounting the curb) are 7-feet of porous, or pervious, surfaces to accommodate parked vehicles. This strategy creates a safe environment for the pedestrian, or kids playing, and a generous buffer between the sidewalk and vehicular traffic. Cost savings for the developer in street widths allow for greater amenities within a neighborhood, which could include additional parks, more street trees, enhanced landscape among many other opportunities.
Bump-outs can also be eliminated in very urban areas (T-4 to T-6) and be better managed with narrower streets or other elements that can effectively create the bump-out. A beautiful and eclectic example of alternatives for bump-outs is in the Historic Old Market District of Omaha, Nebraska. In the Old Market, raised planters act as a bump-out tightening the streets at the intersection, as shown in the image to the right.