Pedestrian Safety Guide and Countermeasure Selection System
Illustration of actual and effective curb radii.
Source: Institute of Transportation Engineers
Curb radii designs are determined based on the design vehicle of the roadway (i.e. the types of vehicles using the roadway, such as buses, tractor trailer trucks, fire trucks, etc.). The most important factor for design is using the “effective radius” rather than the “actual radius” to accommodate the chosen design vehicle. Actual curb radius refers to the curvature along the curb line; effective radius refers to the curvature vehicles follow when turning. Larger effective curb radii can be achieved by adding on-street parking, bicycle lanes, or striping advance stop lines on the destination street of multilane roadways.
The smallest practical actual curb radii should be chosen based on how the effective curb radius accommodates the design vehicle. An actual curb radius of 5 to 10 feet should be used wherever possible. An appropriate effective radius for urban streets with high volumes of pedestrians is 15 to 20 ft. For arterial streets with a substantial volume of turning buses and/or trucks, an appropriate effective curb radius is about 25 to 30 ft. Typically the maximum desired effective curb radius is 35 feet for large vehicles. Tighter turning radii are particularly important where streets intersect at a skew. Corners characterized by an acute angle may require a slightly larger radius to accommodate larger vehicles; corners with an obtuse angle should have the smallest feasible radius to prevent high-speed turns.
Authors and Acknowledgements