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):

R=

+

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

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