There are many factors to be considered when selecting the alignment of roads. These factors also vary according to the type of roads and the areas through which these roads pass.
The factors governing the alignment of roads in plain areas are as follows:
1. class and purpose
The alignment of the road can be decided keeping in view the category and purpose of the road. National and state highways should be aligned as straight as possible between two stations whereas in case of other types of roads, deviation may be allowed where necessary.
2. mandatory marks
Roads are basically built for the development of the areas. Their alignment must necessarily pass through important towns, clusters of villages and places of religious, social, political and commercial importance.
3. type of vehicular traffic
Alignment should be provided according to the type of vehicular traffic. In case of high speed traffic, the road alignment should be as straight as possible whereas in case of bullock cart, tonga etc., the alignment may also have sharp turns.
The alignment of roads should be selected so that the longitudinal slopes are not steeper than the ruler gradient. To achieve this, the alignment may require a deviation from the straight line.
5. horizontal curve
Wherever necessary, the alignment of roads should be provided with flat curves. In the case of National and State Highways, the radius of the horizontal curve should not be less than 230 m. The alignment has to be changed to have a minimum radius.
6. sight distance
The alignment of roads should be such that minimum visual distance is available to the drivers of the vehicles.
The alignment of roads is decided keeping the constraints in mind. For example, the alignment should be changed to avoid marshy land, ponds, wells, cemeteries, historical monuments and religious places etc.
8. cross drainage works
The alignment should be adjusted so that the minimum number of cross drainage works are required. To achieve this, alignment should be chosen with the watershed line, if possible.
When crossing a river, the sites must provide all the necessities needed for a good bridge construction. Road alignment 90. but must cross the river0 To avoid the construction of slant bridge.
10. railway crossing
A road alignment should be given to the railways preferably 90. must cross over0,
1 1 formation bed
The selected alignment should be through areas that provide good formation bedding.
12. earth work
The alignment should be changed where necessary, to avoid excessive cutting and filling.
13. agricultural land and dense forest
The alignment of roads should be fixed so as to avoid costly agricultural land and dense forests for land acquisition.
14. Existing Right of Way (ROW)
In case of upgradation of the road, its existing right should be used to reduce the cost of land acquisition.
15. public demand
The selected alignment of the road should meet the demand of the people of the area.