14
Design Elements
General Guide to RoadPlus - 4.0.0en
1.
P = L / (G
out
- G
in
)
2.
P = (S - S
0
)
2
/ 2(H - H
0
)
3.
P = 1 / 2a
Parameter P
- is the reciprocal of the rate of change of grade
in the vertical curve. Three formulas for the calculation of P
exist:
L
length as horizontal distance from the beginning to the
end of the vertical curve
G
in
grade of the vertical alignment at the beginning of the
vertical curve
G
out
grade of the vertical alignment at the end of the curve
G
in
and
G
out
in decimal units (not percent) negative for
decreasing elevation with increasing station.
S
any station (chainage) on the parabola
S
0
station (chainage) of the high/low point of the parabola
H
height at any station S of the parabola
H
0
height of the high / low point of the parabola
whereas a is a parameter in the general equation for a
parabola in mathematics Y = aX
2
+ bX + c.
Y
elevation of vertical curve above datum
X
horizontal distance from the beginning of the vertical
curve
a
one half of the rate of change of grade in the vertical
curve
b
Grade of the vertical alignment at the beginning of the
vertical curve
c
elevation above datum at the beginning of the vertical
curve
