AdvancedTopic 93 of 112Civil & Structural
Highway geometric design
Sight distance, curves and gradients ensure safety and comfort.
In depth
Design speed governs minimum radius R=V²/(127(e+f)), sight distances (stopping, overtaking), superelevation, gradients, vertical curves and cross-section. Transition curves (clothoid) ease changes in curvature. Balance safety, cost and terrain.
Key points
- Stopping sight distance=reaction+braking
- K-value for crest curves
- Lane widths 3.5 m
ExampleA 100 km/h road needs about 200 m of stopping sight distance.
Highway geometry sets the sight distance, curvature and gradient, which control safety and comfort for every driver.
What is Highway geometric design?
Sight distance, curves and gradients ensure safety and comfort.
Why is it important to understand highway geometric design?
Highway geometry sets the sight distance, curvature and gradient, which control safety and comfort for every driver.
What is stopping sight distance?
The distance needed for a driver to see a hazard and stop safely, which depends on speed, reaction time and braking.
Why does design speed matter?
It sets the minimum curve radius, sight distances and gradients, so the whole road is designed around it.
How is Highway geometric design used in practice?
Typical applications include setting the stopping sight distance on a crest curve, designing a horizontal curve for a design speed of 100 km/h and limiting the gradient of a hill for heavy vehicles.
What should I learn before Highway geometric design?
Study "Transportation planning" first (topic 92 of 112 in Civil & Structural). It covers the groundwork this topic builds on.
What are the key points of Highway geometric design?
Stopping sight distance=reaction+braking. K-value for crest curves. Lane widths 3.5 m.
Can you give an example of Highway geometric design?
A 100 km/h road needs about 200 m of stopping sight distance.
What comes after Highway geometric design?
The next topic is "Pavement design", which builds directly on this one.
How difficult is Highway geometric design?
It is classed as Advanced in Civil & Structural (topic 93 of 112). It is an advanced topic. It assumes you are comfortable with the intermediate topics in Civil & Structural.