3. Reverse curve

a. General

A reverse curve consists of two consecutive tangent curves with radius points on opposite sides of the center line. Figure 15 shows basic nomenclature and parts.

Figure D-15


The PRC is the Point of Reverse Curvature, and is the EC of the first curve and BC of the second.

The distance from PI1 to PI2 is T1 + T2. Because of this relationship, as soon as one curve's geometry is fixed, so is the other's. This makes a reverse curve generally easier to compute than a compound curve.

Once the geometry of both curves are fixed, they can be computed as individual simple curves.

b. Stationing

Stationing can be a little confusing since there can be a station equation at both the PRC and EC of the second curve. Usually, if a stationing is maintained along the tangents, then a station equation only appears at the end of the reverse curve.

To compute stationing:

RC10a            Equation D-6
RC10b   Equation D-7
RC10c   Equation D-8
RC10d   Equation D-9


b. Example

For a reverse curve, the first PI is at 33+50.15 with a 75°20'00"L deflection angle and second PI is at 40+16.70 with a 83°50'00"R deflection angle.

The first curve has a 375.00' radius. Determine the radius of the second curve.