Some useful tips on geometric design of highway
Sight distance: Stopping sight distance, overtaking sight distance, set - back from obstructions.
To avoid accidents & maintain smooth operation of the vehicles in highway, the driver should have the capability to view a long section of road in advance. Therefore, the obstacles will be evidently observable to the driver some distance in advance.
So sight distance is described as the distance within which the operator of a vehicle from a particular height over the carriageway running at design speed contains an apparent, unobstructed view of surface pavement beforehand concerning an object of a specific eight standing on it. From these experiments, it is found that that the scopes of accidents were minimized with the enhancement of the vision.
Sight distance is based on the following factors:
• Road attributes and terrain
• Traffic condition
• Position of obstruction
• Height of driver from the carriageway
• Height of the object over the road surface
• Type of curve
Road conditions with limitations in sight distance.
Limitations exist because of the reasons given below:
1. Horizontal curves: Limitation in the horizontal curve occurs because of obstacles within the curve made by building, trees and cut slope or the incapability to enlighten the head light beam along the curved alignment at the inside of the curve.
2. Vertical summit curves: Perceptibility of a road surface on the other side of the summit curve is affected in peaks. Although perceptibility conditions are examined for the gradient of the curve, it should also be verified in night conditions.
3. Vertical valley curves: Perceptibility in the valley curves isn’t affected throughout day time but in night driving it creates great issues.
4. Intersections: At intersections also, need for visibleness may also be considerably reduced if obstacles like buildings, greeneries arise inside the area are called as sight triangle.