Chapter 4 - Elements of Design

4.2. Horizontal Alignment

The location and alignment selected for a highway are influenced by factors such as physical controls, environmental considerations, economics, safety, highway classification and design policies. The horizontal alignment cannot be finalized until it is coordinated with the vertical alignment and cross section elements of the roadway.

Horizontal curves shall be used for all deflections in a horizontal alignment, with the exception of alignment changes without horizontal curves as discussed in detail in Section 4.2.2. Types of Curves of this Manual. In special situations, such as roadway reconstruction or widening on existing alignment, practicality will dictate when deflection angles (PI without a curve) may be introduced in lieu of horizontal curvature. Spiral curves are generally not utilized on Georgia roadways.

Refer to the AASHTO Green Book Chapter 3, Elements of Design when determining the radii of horizontal curves and corresponding superelevation (if applicable). Wherever possible, minimum curve radii and maximum superelevation rates should be avoided for any given speed design.