4.7.2 Curve Radius

The design of roadway curves should be based on an appropriate relationship between design speed and curvature as well as their joint relationships with superelevation rate and side friction. The minimum radii of curves are important control values in designing for safe operation. Design guidance for low-speed rural town, suburban, urban, and urban core facilities (45-mph and below) is shown in
Table 4-4
. Design guidance for curvature of highspeed (50-mph and above) or rural context facilities is shown in
Table 4-5
,
Table 4-6
and
Table 4-7
for maximum superelevation (e
max
) rates equal to 4 percent, 6 percent, and 8 percent respectively.
For high-speed design conditions, the maximum allowable deflection angle without a horizontal curve is 30 minutes.
For low-speed design conditions, the maximum allowable deflection angle without a horizontal curve is 1 degree.