Road alignment refers to the positioning of the center line of a highway on the ground. Put simply, it’s the direction the road takes. This is also known as highway alignment. There are two main types:
Horizontal alignment comprises three components:
Vertical alignment includes:
This aspect of road construction is crucial. Choosing the right alignment can prevent various issues, including increased costs, maintenance expenses, vehicle operation costs, and a higher likelihood of accidents.
Several factors play a role in determining the alignment of a road:
1. Availability of Construction Materials : Materials needed for road construction should be easily accessible near the construction site. This reduces construction and maintenance costs, as well as transportation expenses.
2. Obligatory Points :
These are critical points that guide the highway’s alignment. They fall into two categories:
i) Points where an alignment is allowed to pass (e.g., bridge sites, important cities).
ii) Points where an alignment should not pass (e.g., religious sites, water bodies, monuments).
3. Lower Grades and Easy Curves : The chosen alignment should aim for low grades and gentle curves. Achieving this may require a longer road, but it ensures smoother travel.
4. Crossings : Consideration must be given to crossings like streams, rivers, and railways along the road’s alignment.
5. Geological Features : The road’s alignment should account for geological features in the surrounding area, such as soil stability, landslide risks, etc.
6. Proper Drainage : Adequate drainage, especially for rainwater, is crucial for road stability. Factors like subsurface water levels and high flood levels must be considered.
7. Traffic : The alignment should meet traffic requirements. Studying traffic patterns, origin-destination flow, and future traffic forecasts is essential.
8. Economy :Economic considerations are vital. Minimize construction, maintenance, and operation costs without compromising quality.
9. Miscellaneous Factors
For a road’s alignment to be considered ideal, it should possess the following qualities:
1. Short : The alignment should be as short as possible between two terminal stations. Straight alignments are typically the shortest, reducing construction and travel time.
2. Easy : The alignment’s design should simplify construction, maintenance, and vehicle operation with manageable curves and gradients.
3. Safe : Safety standards for vehicles on the road should be met. Avoid steep curves, as gradual ones are safer and reduce the risk of accidents.
4. Economical : The alignment should minimize construction, maintenance, and operation costs while maintaining quality work.
