Stopping site distance, Overtaking sight distance and Sight distance at intersections are important to study and check for the design of the highways.
Sight distance at the intersections:
IRC recommends that at non-controlled intersections, sufficient visibility should be provided such that sight distance on each road is at-least equal to SSD corresponding to the design speed of the road.
IRC recommends that a minimum visibility distance of 15 m along the minor road and a distance of 220, 180, 145 and 110 m along the major road corresponding to design speeds of 100, 80, 65 and 60 kmph. respectively may be provided.
Apart from three situations above, following sight distances are considered by IRC in highway design.
- Intermediate sight distance(ISD) = 2.SSD
When overtaking sight distance cannot be provided, intermediate sight distance is provided to give limited overtaking opportunities to fast vehicles.
- Head light sight distance
This is the distance along the road, visible to a driver during the night driving under the illumination of the vehicle head lights. This sight distance is critical at up-gradients and at the ascending stretch of the valley curves.
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