Stopping Sight Distance
The sight distance available on a road to a driver at any instance depends on :
(i) features of the road ahead.
(ii) height of the driver‘s eye above the road surface.
(iii) height of the object above the road surface.
The feature of the road ahead which affect the sight distance is the horizontal alignment and vertical profile of the road, the traffic condition and the position of obstructions. At vertical summit curves, the height of the driver‘s eye and the object above road level are more important factors affecting the visibility. The height of an object to be considered for stopping a vehicle depends on what might be a source of danger to the moving vehicle. For the aim of mensuration the stopping sight distance or visibility ahead. IRC has suggested the height of eye level of the driver as 1.2 m and the height f the object as 0.15 m above the road surface.
Hence the stopping distance available at a summit curve is that distance measured along the road surface at which an object of height 0.15 m can be seen by a driver where the eye is at a height of 1.2 m above the road surface fig
The distance within which a motor vehicle can be stopped depends upon the factors listed below:
(a) The total reaction time of the driver
(b) Speed of vehicle
(c) Efficiency of brakes
(d) Frictional resistance between the road and the types
(e) The gradient of the road.