Chapter 4 - Elements of Design

4.4. Combined Horizontal and Vertical Alignments

4.4.1. Aesthetic Considerations

Coordination of the horizontal and vertical alignment can result in a highway that is visually pleasing. This can be achieved in several ways: 

• A sharp horizontal curve should not be introduced at or near the low point of a sag vertical curve, which produces a distorted appearance.

• There should be a balance between curvature and grades. The use of steep grades to achieve long tangents and flat curves, or the use of excessive curvature to achieve flat grades, are considered poor design. A logical design is a compromise between the two conditions. Wherever feasible the roadway should “roll with” rather than “buck” the terrain.

• If possible, every effort should be made to line up points of vertical intersection (PVI’s) with horizontal points of intersections (PI’s) and to maintain consistency between the horizontal and vertical curve lengths. Vertical curvature superimposed on the horizontal curvature generally results in a more visually pleasing facility. Successive changes in profile not in combination with horizontal curvature may result in a series of dips not visible to the driver. If PVI’s and PI’s cannot be made to coincide, the horizontal curvature should “lead” the vertical curve and the horizontal curve should be slightly longer than the vertical curve in both directions.

• A balanced design which provides horizontal and vertical alignments in the middle range of values is preferable to allowing either horizontal or vertical to become extreme in order to optimize the other.

• Design the alignment to enhance attractive scenic views of the natural and manmade environment, such as rivers, rock formations, parks, and outstanding buildings.

• In residential areas, wherever possible, design the alignment to minimize nuisance factors to the neighborhood. Generally, a depressed facility makes a highway less visible and less noisy to adjacent residents. Minor horizontal adjustments can sometimes be made to increase the buffer zone between the highway and clusters of homes.

• Refer to the GDOT Context-Sensitive Design Online Manual for additional information