This tutorial demonstrates how to create and edit layout profiles, which are often called design profiles or finished grade profiles.
A layout profile represents a proposal for a road or other designed surface. This type of profile is always drawn on the grid of a profile view, which usually displays the surface profile along the same horizontal alignment.
A layout profile includes the following elements:
- Straight line tangents with specified grade or slope.
- Points of vertical intersection (PVI) where tangents meet.
- Vertical curves that are usually parabolic in shape. Vertical curves can also be circular or asymmetrical parabolic.
Vertical curves can be one of two basic types: crest curves or sag curves.
- A crest curve exists at a hilltop, or wherever the incoming tangent has a higher grade than the outgoing tangent. There are three types of crest curves: a positive to negative grade transition, positive to positive, and negative to negative. The point of vertical intersection (PVI) of a crest curve is above the curve.
- A sag curve exists at the bottom of a valley, or wherever the incoming tangent has a lower grade than the outgoing tangent. There are three types of sag curves: a negative to positive grade transition, negative to negative, and positive to positive. The PVI of a sag curve is below the curve.
The vertical curves on a layout profile can be designed in relation to engineering speed tables for safe vehicular travel at a particular maximum speed. Other tables can be used to design vertical curves so that the distance illuminated by the headlights of a vehicle at night is always greater than the stopping distance at the maximum design speed.