Special Considerations while aligning Highways on hilly areas
Iamcivilengineer
Sunday, August 13, 2017
Articles
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Civil Engineering Terminologies
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Highway Engineering
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Terminologies
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Transportation Engineering
The position or the layout of the center line of the highway on the ground is called the alignment. The horizontal alignment includes the straight path, the horizontal deviations and curves.
Changes in gradient and vertical curves are covered under vertical alignment of roads.
A new road should be aligned very carefully as improper alignment would result in one or more of the following disadvantages :-
Once the road is aligned and constructed, it is not easy to change the alignment due to increase in cost of adjoining land and construction of costly structures by the road side. Hence the importance of careful considerations while finalizing the alignment of a new road need not be over emphasized.
Numerous hill side drains should be provided for adequate drainage facility across the road. But the cross drainage structure being costly, attempts should be made to align the road in such a away where the number of cross-drainage structures are minimum.
Different sets of geometric standards are followed in hill roads with reference to gradient, curves and speed and they consequently influence the sight distance, radius of curve and other related features. The route should enable the ruling gradient to be attained in most of the length, minimizing steep gradients, hair pin bands and needless rise and fall.
Changes in gradient and vertical curves are covered under vertical alignment of roads.
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| Highway Leading through mountains towards National Park Canada |
A new road should be aligned very carefully as improper alignment would result in one or more of the following disadvantages :-
- Increase in construction cost
- Increase in maintenance cost
- Increase in vehicle operation cost
- Increase in accident rate
Once the road is aligned and constructed, it is not easy to change the alignment due to increase in cost of adjoining land and construction of costly structures by the road side. Hence the importance of careful considerations while finalizing the alignment of a new road need not be over emphasized.
Stability
While aligning hill roads, special care should be taken to align the road along the side of the hill which is stable. A common problem in hill roads is that of land slides. The cutting and filling of earth to construct roads on hill-side causes steepening of existing slopes and effect its stability.Drainage
Numerous hill side drains should be provided for adequate drainage facility across the road. But the cross drainage structure being costly, attempts should be made to align the road in such a away where the number of cross-drainage structures are minimum.
Geometric standards of hill roads
Different sets of geometric standards are followed in hill roads with reference to gradient, curves and speed and they consequently influence the sight distance, radius of curve and other related features. The route should enable the ruling gradient to be attained in most of the length, minimizing steep gradients, hair pin bands and needless rise and fall.
