PC
PT
C
L
Road
Tape
C = centerline
L
PC = point of curvature
PT = point of tangency
Figure 1-6. Using a Tape to Determine the Radius of Curvature
(2) Another method is to use the radius-of-curvature formula. Refer to the
following formula and Figure 1-7 (Always round your answer down to the next whole
number):
c2
M
R=
+
8M
2
where--
R = radius of curvature (always round down to the next whole number)
c = chord (sometimes referred to as tape) (the distance from the centerline of the road to
the centerline of the road at the outer extremities of the curve)
8 = conversion and correction factor
M = median (the perpendicular distance from the center of the chord to the centerline of
the road). A 90, angle must be formed at M and c.
2 = conversion and correction factor
C
M
L
90
c
R
R
c = chord (distance to C from C )
L
L
c2
C = centerline
M
L
R=
+
M = median (midpoint of c)
8ƒM
2
R = radius
Figure 1-7. Using a Formula to Determine the Radius of Curvature
EN 5622
1-6
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