The center line layout or position on the ground surface is called Alignment.There are two types of Alignments horizontal Alignment and Vertical Alignment.
Horizontal Alignment includes the straight path,curves or deviation in horizontal direction.
Vertical Alignment includes vertical curves and gradient on the ground.
But it is difficult to change the alignment once the road is construction, so care has to be taken in finalizing the alignment.
Basic Requirement of an Ideal Alignment
- It should have a shortest path.
- The alignment must be easy to construct and maintain and also it should be easy for vehicle operation.
- It should be safe in case of designing the horizontal and vertical curves.
- The alignment should be selected in such a way that it is economical during construction.
Factors Controlling Alignment
- These are control points governing the alignment of Highways.
- Points through which the Alignment has to pass
- Hill Pass
- Location of Bridge
- Connecting Intermediate Town
- Avoiding an Intermediate Area
- Points through which the Alignment should not pass
- If it is a case of religious place like temple, mosque, church ,grave etc. The Alignment should not pass as per law.
- Alignment should be selected based on traffic surveys. Origin and Destination study should be carried out in that area and also we have to consider the future development in that road network.
- Alignment is decided based on the design of horizontal and vertical curves, sight distance and gradient of that section. It is also decided based on the Design Speed of that Highway.
- It is based on the initial cost of construction and maintenance cost of the road, if it a shortest path the cost of construction will be reduced.(Decision is based on Quantity of Cutting and Filling of Earth.)
- Common problems in hill roads are land sliding, stability of road, providing adequate drainage facility, reducing hairpin bends, needless raise and fall.