RPCPTFigure 11-3.—Elements of a horizontal curve.center of the circle (O) to the PC and PT. Thevalue of the central angle is equal to the I angle.Some authorities call both the intersectingangle and central angle either I or A.RADIUS. The radius of the circle of which thecurve is an arc, or segment. The radius isalways perpendicular to back and forwardtangents.POINT OF CURVATURE. The point of curva-ture is the point on the back tangent where thecircular curve begins. It is sometimesdesignated as BC (beginning of curve) or TC(tangent to curve).POINT OF TANGENCY, The point oftangency is the point on the forward tangentwhere the curve ends. It is sometimesdesignated as EC (end of curve) or CT (curveto tangent).POCLTLC11-3POINT OF CURVE. The point of curve is anypoint along the curve.LENGTH OF CURVE. The length of curve isthe distance from the PC to the PT, measuredalong the curve.TANGENT DISTANCE. The tangent distanceis the distance along the tangents from the PIto the PC or the PT. These distances are equalon a simple curve.LONG CHORD. The long chord is thestraight-line distance from the PC to the PT.Other types of chords are designated asfollows:CThe full-chord distance between adja-cent stations (full, half, quarter, or one-tenth stations) along a curve.c]The subchord distance between the PCand the first station on the curve.
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