The maximum safe speed of vehicles assumed for a geometrical design of a highway is known as design speed.
The design speed dependent upon the following factors
1. Types and conditions of the road surface.
2. Structure of the road.
3. Nature and intensity of traffic.
4. Types of the curve along the road.
5. Sight distance required.
6. Nature of the country.
The design speed is the most important factor controlling the geometric design elements of highways, the design speed is decided considering the overall requirements of highways.
In India, different speed standards have been assigned depending upon the importance, or class of the road.