FIGURE 16. Compound curve.and 800 ft (243.8 m), as shown in Fig. 16. The minimum allowable radius is 1000 ft
(304.8 m). Compute the larger radius and the two central angles.
Calculation Procedure:
- Calculate the latitudes and departures of the known sides
A compound curve is a curve that comprises two successive circular arcs of unequal radii
that are tangent at their point of intersection, the centers of the arcs lying on the same side
of their common tangent. (Where the centers lie on opposite sides of this tangent, the
curve is termed a reversed curve). In Fig. 16, C is the point of intersection of the arcs, and
DE is the common tangent.
This situation is analyzed without applying any set equation to illustrate the general
method of solution for compound and reversed curves. There are two unknown quantities:
the radius R 1 and a central angle. (Since A 1 + A 2 = A, either central angle may be consid-
ered the unknown.)
If the polygon A VBO 2 O 1 is visualized as a closed tr^/erse, the latitudes and departures
of its sides are calculated, and the sum of the latitudes and sum of the departures are
equated to zero, two simultaneous equations containing these two unknowns are obtained.
For convenience, select O 1 A as the reference meridian. Then