The Location module supports circular curves and spiral curves.
A horizontal curve is defined by the point of intersection (IP ) of two tangent lines. The Begin Curve and End Curve (BC and EC) points are inserted at the time the curve is created and can not be edited by the user except through the use of the Horizontal Curves Panel.
To create a horizontal curve:
1. Create two horizontal alignment segments that define the road center line before and after the curve (see Interactive Operations).
3. Click on the IP with the selection tool. The "Current Point is not an IP" message will disappear and the Circle item can now be turned on.
4. Type in the radius parameter. If the value you type in is larger than the maximum allowable radius, a warning message will be displayed.
5. After pressing Apply, the Location module generates BC / EC points and updates the earthworks at the affected points. Steps 3,4,5 can be used as many times as necessary to change the radius of existing curves.
2. Click on the EC of the curve you want to edit. The curve parameters will appear in the Horizontal Curves Panel and be available for edit. Then select No Curve and press Apply.
Switch Backs
Horizontal curves that change direction by much more than 90 degrees will require at least two curves and three tangents (this is true of switch back curves).
Figure 1. Switch Back Curves
Road Edges
You may notice after creating a curve that the road edges do not follow the curve. This is because road edges are calculated between cross sections and the curve may only have cross sections at the BC and EC points. To rectify this problem create reporting points around the curve (see Edit - Auto Generate).
