Crest Vertical Curves
The following excerpt was taken from the 1994 edition of
AASHTO's A Policy on Geometric Design of Highways and Streets (p. 282).
Minimum lengths of crest vertical curves as determined by sight distance
requirements generally are satisfactory from the standpoint of safety, comfort, and
appearance. An exception may be at decision areas, such as sight distance to ramp exit
gores, where longer lengths are necessary. Refer to the section in this chapter concerning
decision sight distance.
The basic formulas for length of a parabolic vertical curve in
terms of algebraic difference in grade and sight distance follow:
When S is less than L,
When S is greater than L,
Where:
L = length of vertical curve, m;
S = sight distance, m;
A = algebraic difference in grades, percent;
h1 = height of eye above roadway surface, m (normally 1070 mm/1000 mm/m)
h2 = height of object above roadway surface, m (normally 150 mm/1000 mm/m)
(The heights h1 and h2 given above correspond to the stopping sight
distance.)
|