Geometric Design - Vertical Curves Flashcards
Factors that influence highway design
Sight distance
Stopping sight distance of vertical curves
Decision sight distance
Passing sight distance
Criteria for measuring sight distance
Height of driver’s eye (3.5ft)
Height of object (2.0ft)
Stopping sight distance is sum of two distances:
Brake reaction distance
Braking distance
Two types of vertical curves in stopping sight distance
Crest vertical curves
Sag vertical curves
(depends on headlight sight distance, rider comfort, drainage control)
Where is decision sight distance important?
Interchange and unusual intersections
Toll plazas and lane drops
High demand areas with “visual noise”
How is passing sight distance determined?
By basis of length needed to safely complete a normal passing manuever
What does horizontal alignment include?
Straight and curved paths
What does vertical alignment include?
Level and gradients
Why is road alignment important?
Because bad alignment enhances construction, maintenance, and vehicle operating cost. Also difficult to change once its in.
Methods used to model terrain surfaces
Points and break lines
Triangulated Irregular Networks (TIN)
Contours
Grids
Horizontal alignment consists of…
Series of straight line tangents connected to circular and transition curves
Vertical alignment consists of…
Series of straight grades joined by vertical curves. Species elevation along roadway
