Chapter 4 - Elements of Design

4.5. Superelevation

4.5.2. Sharpest Curve without Superelevation

Although superelevation is advantageous for high-speed traffic operations, various factors combine to make its use impractical in many built-up areas. Such factors include:

• wide pavement areas
• need to meet grade of adjacent property
• surface drainage considerations
• frequency of cross streets, alleys and driveways
• at major intersections or other locations where there is a tendency to drive slowly because of turning and crossing movements, warning devices, and traffic signals

The minimum curve radius is a limiting value of curvature for a given design speed and is determined from the maximum rate of superelevation and the maximum side friction factor selected for design. Very flat curves need no superelevation. In many instances, it is desirable to maintain a normal crown typical section on the roadway. In these cases, implementation of a curve with a radius flat enough as to not require superelevation should be considered.