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.