MODULE 3: Vertical Alignment of Highways Flashcards
provides a smooth transition between two tangent grades.
vertical curve
two types of vertical curves:
crest vertical curves and sag vertical curves
Properties of Parabolic Vertical Curves:
a) The rate of change of grade on a vertical curve is constant.
b. Tangents drawn from any two points on a vertical axis parabola always intersect
midway between the points of tangency.
c. Vertical offsets from a tangent to a parabola are proportional to the squares of
the distances from the point of tangency.
d) If a tangent to the parabola is drawn between the main tangents, the horizontal
projection of the intercept cut off on this new tangent by the main tangents is equal
to one-half of the horizontal projection of the long chord of the parabola.
Two sight distances have been discussed in connection with horizontal alignments:
these two sight distances are the major factors in determining the required length of
vertical curves.
the stopping sight distance and the passing sight distance.
For _____, h1 pertains to the driver’s eye height and h2 is the height of the object (hazard) seen along the path of the vehicle
SSD
For _____, h2 is taken as the height of the roof of the vehicle coming in the opposite direction when the first vehicle initiates its overtaking
maneuver
PSD
Given the requirements for sight distances ,the required length of the crest vertical curve may be obtained by considering the following two cases:
a. The sight distance is shorter than the required length of curve
b. The sight distance is longer than the required length of curve
Along an open highway, the length of _______________ is usually based on the length of the road illuminated by the headlight beam at night.
sag vertical curves
two cases in Sight Distances at Sag Vertical Curves
a. Sight distance is shorter than the required length of curve
b. Sight distance is longer than the required length of curve
