Chapter 4 - Elements of Design

4.3. Vertical Alignments

GDOT uses design controls for crest and sag vertical curves based on sight distance . The AASHTO Green Book Chapter 3, Elements of Design, provides additional discussion on rates of vertical curvature (K). Maximum allowable vertical grades are dependent on the classification of the facility and are discussed in the following AASHTO Green Book chapters:

• Chapter 5. Local Roads and Streets
• Chapter 6. Collector Roads and Streets
• Chapter 7. Rural and Urban Arterials
• Chapter 8. Freeways

GDOT has adopted the AASHTO desirable values for maximum and minimum vertical grades.

GDOT typically uses symmetrical parabolic vertical curves at changes in grade. Exceptions to this include spot locations such as alignment breaks near intersections and overlay transitions where vertical grade breaks can be accomplished without the use of vertical curves. The maximum grade break (%) varies based on the design speed of the facility.