The position of the layout of the centre line of the highway on the ground is called the alignment.
There are two types of alignment :
1) Horizontal alignment :
It includes :
i) Straight Path
iii) Horizontal deviators
2. Vertical alignment :
It includes :-
i) Vertical Curves (Summit curves, valley curves)
ii) Vertical Gradients
The alignment of road should be carefully decided before the construction of road is started.
Improper alignment would result in one or more of the following disadvantages :
i) Increase in construction cost
ii) Increase in maintenance cost
iii) Increase in Vehicle Operation cost
iv) Increase in accident rate
REQUIREMENTS OF GOOD ALIGNMENT
The basic requirement of an ideal alignment are :
1) Short :
It is desirable to have a short alignment between two terminal stations.
A straight align ment would be the shortest.
Such a route will be cheap in construction and will reduce the time of travel.
2) Safe :
The alignment should be safe enough for construction and maintenance.
Also it should be safe for the traffic operation with safe geometric features.
3) Easy :
The alignment should be such that it is easy to construct and maintain the road with minimum problems.
Also the alignment should be casy for the operation of vehicles with easy curves and gradients.
4) Economical :
The highway alignment should be selected in such a way that the total cost including initial cost, maintenance cost and operation cost is brought down to the minimum level.