Clear Zones and Curves

The clear zone values given on the previous slide assume a tangent alignment. Horizontal curves may increase the angle of departure from the roadway and thus increase the distance the vehicle will need to recover. Desirably and if practical, the designer should adjust the tangent values to provide wider clear zones on the outside of horizontal curves. To determine the desirable clear zone on the outside of a horizontal curve, multiply the clear zone distance (determined from the previous slide) by the appropriate curve correction adjustment factor for the speed and radius of the curve (as shown below). No adjustments are warranted for curve radii greater than 2950 ft.

Horizontal Curve Adjustments*
(Clear zone curve corrections)