Week 7 - Vertical Curve Geometry

When the profile line increases from level terrain, what is it called?

Positive (plus) grade

When the profile line decreases from level terrain, what is it called?

Negative (minus) grade

What are the two main categories of vertical curves?

Crest curves and Sag curves

What type of vertical curve is shown when grades go from +g₁ to −g₂?

Crest vertical curve

What type of vertical curve is shown when grades go from −g₁ to +g₂?

Sag vertical curve

What does PVI stand for?

Point of Vertical Intersection

What does PVC stand for?

Point of Vertical Curvature

What does PVT stand for?

Point of Vertical Tangency

Where are vertical curves typically centered?

At the PVI

What shape are vertical curves?

parabolic

What assumption is made about tangent lengths in vertical curves?

Equal tangent length

What is usually the controlling factor for crest vertical curves?

Stopping sight distance (SSD)

What does SSD determine for crest curves?

Minimum curve length based on grades and design speed

What is A in vertical curve equations?

=G1​−G2​

What condition defines Case 1 for crest curves?

S < L

What condition defines Case 2 for crest curves?

S > L

What does SSD stand for?

Stopping Sight Distance

What is the standard driver reaction time used?

2.5 seconds

What is G often assumed in SSD equations?

0

Why is G often assumed to be 0 in SSD for vertical curves?

Because stopping could occur on positive grade, negative grade, or within the curve

What is the controlling factor for sag vertical curves?

Headlight projection distance

What condition defines Case 1 for sag curve?

S < L

What condition defines Case 2 for sag curves?

S > L

Given G₁ = 7% and G₂ = −3%, what type of curve is this?

Crest curve

Given G₁ = −7% and G₂ = 3%, what type of curve is this?

Sag curve