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.