Requirements of ideal highway alignment

The alignment of a highway is the position of its centre line on the ground. An ideal alignment should be short, easy, safe and economical (the four basic requirements).

Requirements

1. Short: a straight line is the shortest route; a short alignment saves construction and vehicle operating cost.
2. Easy: gentle gradients and flat curves, so that vehicles can run smoothly at the design speed. The gradient should not exceed the ruling gradient.
3. Safe: adequate sight distance; no sharp curves, steep grades or unstable slopes; safe at intersections and bridges; geometric design standards (NRS 2070) followed.
4. Economical: low initial cost (earthwork, structures) as well as low maintenance and vehicle operating cost; cut and fill balanced.
5. Serves the needs: passes through or near the important towns and traffic-generating points.
6. Stable ground: avoids landslide-prone, flood-prone, marshy and poor-soil areas.
7. Minimum cross-drainage works: crosses streams at right angles and at narrow, stable points, with fewer bridges and culverts.
8. Construction materials: available near the alignment.
9. Minimum land acquisition, avoiding religious and historical sites and forests as far as possible.
10. Future expansion: allows widening and upgrading.
11. Hill roads: follow the contours, use hairpin bends where necessary, and avoid steep, wet north-facing slopes.