Page 346 - Civil Engineering Formulas

HIGHWAY AND ROAD FORMULAS 277

1
C 2R sin 2 I exact (11.5)
100I
L exact (11.6)
D
L 3 C 3
L C approximate (11.7)
24R 2 24R 2
Dl
d exact for arc definition (11.8)
100
Dc
approximate for chord definition (11.9)
100
d c
sin exact for chord definition (11.10)
z 2R
c 2
a approximate (11.11)
2R
c 2
b approximate (11.12)
R

PARABOLIC CURVES

Parabolic curves are used to connect sections of highways or railroads of differ-
ing gradient. The use of a parabolic curve provides a gradual change in direction
along the curve. The terms and symbols generally used in reference to parabolic
curves are listed next and are shown in Fig. 11.3.

PVC point of vertical curvature, beginning of curve
PVI point of vertical intersection of grades on either side of curve

L L
2 2
PVI
(elev. V)

G 1 X Elev. E x
G 2
L

PVC (elev. E 0 ) )
PVT (elev. E t
FIGURE 11.3 Vertical parabolic curve (summit curve).