Curb Radius Reduction:

One of the common pedestrian crash types involves a pedestrian who is struck by a right-turning vehicle at an intersection. A wide curb radius typically results in high-speed turning movements by motorists. Reconstructing the turning radius to a tighter turn will reduce turning speeds, shorten the crossing distance for pedestrians, and also improve sight distance between pedestrians and motorists.

Nearby land uses and types of road users should be considered when designing an intersection so that curb radii are sized appropriately. If a curb radius is made too small, large trucks or buses may ride over the curb, placing pedestrians in danger.

Where there is a parking and/or bicycle lane, curb radii can be even tighter, because the vehicles will have more room to negotiate the turn. Curb radii can, in fact, be tighter than any modern guide would allow: older cities in the Northeast and in Europe frequently have radii of 0.6 to 1.5 m (2 to 5 ft) without suffering any detrimental effects.

More typically, in new construction, the appropriate turning radius is about 4.6 m (15 ft) and about 7.6 m (25 ft) for arterial streets with a substantial volume of turning buses and/or trucks. Tighter turning radii are particularly important where streets intersect at a skew. While the corner characterized by an acute angle may require a slightly larger radius to accommodate the turn moves, the corner with an obtuse angle should be kept very tight, to prevent high-speed turns.



  Purpose
• Safer intersection design.
• Slow right-turning vehicles.
• Reduce crossing distances, improve visibility between drivers and pedestrians, and provide space for accessible curb ramps.
• Shorter crossing distances can lead to improved signal timing.
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  Considerations
• Consider effective radii by taking into account parking and bicycle lanes.
• Make sure that public maintenance vehicles, school buses, and emergency vehicles are accommodated.
• Large trucks and buses may ride over the curb at intersections with tight radii, creating a danger for pedestrians who are waiting to cross.
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  Estimated Cost
Construction costs for reconstructing a tighter turning radii are approximately $2,000 to $20,000 per corner, depending on site conditions (e.g., drainage and utilities may need to be relocated).
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  Case Studies
Bethesda, Montgomery County, MD 
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Adapted from Making Streets That Work, Seattle, 1996

Photo by Peter Lagerwey
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Photo by Dan Burden
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U.S. Department of Transportation Federal Highway Administration