Applicable Countermeasures

Before (top) and after (bottom) curb radius is reduced.

Illustration by A.J. Silva

Photo by Peter Lagerway
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Photo by Dan Burden
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Curb Radii Revisions

Motor vehicles turning at a high rate of speed pose problems for bicyclists (as well as pedestrians). This is a common problem when motorists traveling on an arterial street turn onto a residential street. A typical bicycle-motor vehicle crash type, sometimes called a "right hook," occurs when a motor vehicle passes a bicycle going straight ahead and then turns right shortly after making the passing maneuver. Reducing the radii of curbs at these high speed right turns provides a remedy. Creating 90-degree intersection corners or corners with tight curb radii tend to slow motorists.

Some communities routinely reduce curb radii at locations where the routes: (1) are used by schoolchildren or the elderly, (2) are in neighborhood shopping areas with high bicycle and pedestrian volumes, and (3) are at particular intersections known to have a safety problem (see case study #20). A logical step is to evaluate the curb radii along a corridor frequented by bicyclists, along with a study of the crash types. Care must be used when revising curb radii on routes with truck and bus traffic. If a curb radius is made too small, large trucks and buses may ride over the curb or may veer out into an adjacent traffic lane to make the turn.

When there is parking and/or a bike lane, curb radii can be tighter, because the motor vehicles will have more room to negotiate the turn. Older cities in Europe and in the northeast United States frequently have curb radii of 0.6 to 1.5 m (2 to 5 ft) without suffering any detrimental effects. More typically, however, 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 number 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 turning maneuvers, the corner with an obtuse angle should be kept very tight to prevent high-speed turns.


  • Create a safer intersection design.
  • Slow right-turning motor vehicles.
  • Lessen likelihood of "right hook" crashes.

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  • Where curb radii revision is to be considered, the road or street should be evaluated to determine if appropriate for this facility.
  • Make sure that public maintenance vehicles, school buses, emergency vehicles, and typical trucks and buses can be accommodated.
  • Determine if the presence of on-street parking and/or bike lanes help to tighten the radii more than the norm.

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Estimated Cost

Costs for reconstructing a curb to a tighter radius can vary from approximately $5,000 to $40,000, depending on site conditions (e.g., the amount of concrete and landscaping that is required, whether drain grates and other utilities have to be moved, and whether there are other issues that need to be addressed).

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Case Studies

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