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 bump-out image to the right is another alternative to the conventional bump-out. This alternative leaves an opening along the curb to allow storm water to pass through the bump-out where water is directed into the planting area. The planting area is recessed below the flow line of the curb for infiltration. In the instance of an adjacent accessibility ramp and intersection, a drain inlet should be provided to capture water that is not infiltrated prior to intersecting with the ramp and intersection. On a landscape note, a larger rock mulch should be used in this situation. An organic mulch or a small rock pebble mulch or breeze will be displaced in a large storm in this scenario and should not be used. This bump-out is appropriate and most effective in T-4 (General Urban Zone) and T-5 (Urban Center Zone) along the urban-to-rural transect.
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