---
title: "Short note: superelevation in hill roads"
subject: "Transportation Engineering I"
chapter: 5
key: "semester_6/transportation_engineering_i:super-hill-roads"
source: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/super-hill-roads
site: BCT Engineering
---

# Short note: superelevation in hill roads

Transportation Engineering I · Chapter 5: Hill Roads

- Asked in: 2066 Magh (old course), 4 marks
- Video: [Design consideration for superelevation_Hill roads_ DCE III/II](https://www.youtube.com/watch?v=MPjdnXFRQds) — Jalapa Devi Engineering
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/super-hill-roads
- Whole chapter: https://www.bctengineer.com/md/semester_6/transportation_engineering_i/chapter-5

## Question

Write a short note on superelevation in hill roads.

## Short answer

Superelevation is raising the outer edge to counter centrifugal force. On hill roads, max e = 10% (7% in snow areas), min = camber (2.5-3%). It is attained gradually over the transition length, rotating about the inner edge. On hairpins, full 10% provided with reduced gradient.

## Answer

**Superelevation (cant)** is the raising of the outer edge of the carriageway above the inner edge at a horizontal curve, so that a component of the vehicle's weight balances the centrifugal force.

#### Superelevation on hill roads (IRC:SP:48; NRS 2070 follows)
- The superelevation rate is given by
$$
e + f = \frac{v^2}{127R}
$$
with $v$ in km/h and $R$ in m; $f$ = side friction factor, taken as 0.15.
- **Maximum value**: 10% (1 in 10) on hill roads in non-snow-bound areas; in snow-bound/ice-prone areas not more than 7% (to avoid vehicles sliding at low speed on ice).
- **Minimum**: equal to the camber, 2.5 to 3% (cross-slope of the road surface).
- On a hairpin, the combined gradient (longitudinal grade plus superelevation) must stay within limits, so the longitudinal grade is reduced on the curve.
- **Attainment**: the superelevation is introduced gradually over the length of the transition (or, if there is no transition, 2/3 on the straight and 1/3 on the curve), by rotating the pavement about the **inner edge** (so that the hill-side cut and drain are not affected). The rate of change, i.e. the relative gradient between the raised outer edge and the axis of rotation, should not be steeper than about 1 in 60 in hilly terrain.
- For radii above a limit (when the required $e$ is less than the camber), the road keeps its normal camber section.
- **Extra widening** is provided on sharp curves along with the superelevation.

For a hairpin with a small radius (14 m or so), the full 10% superelevation is provided, the speed is restricted to 20 km/h, and the curve is on a gentle gradient of 1 in 40 maximum.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is the superelevation relation used with v in km/h and R in m?
   A. e + f = v^2/(127R)
   B. e + f = v^2/(9.81R)
   C. e = v/(127R)
   D. e - f = v^2/(127R)
   Answer: A. The equilibrium relation is e + f = v^2/(127R), with f taken as 0.15. (Key point: Superelevation equation)

2. What is the maximum superelevation on hill roads in snow-bound/ice-prone areas?
   A. 10%
   B. 7%
   C. 12%
   D. 2.5%
   Answer: B. It is limited to 7% in snow-bound areas to avoid vehicles sliding inward at low speed on ice, against 10% elsewhere. (Key point: Maximum superelevation)

3. About which edge is the pavement rotated to attain superelevation on hill roads, and why?
   A. Outer edge, to keep the road level
   B. Inner edge, so the hill-side cut and drain are not affected
   C. Centre line, to save earthwork
   D. No rotation is done
   Answer: B. Rotating about the inner edge leaves the hill-side cut and drain undisturbed. (Key point: Axis of rotation)

## Related in Transportation Engineering I

- [Design and construction problems of hill roads](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Ahill-problems) — Transportation Engineering I, chapter 5, asked 11×
- [Typical cross-sections of hill roads](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Ahill-cross-sections) — Transportation Engineering I, chapter 5, asked 9×
- [Surface water drainage in hill roads](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Ahill-surface-drainage) — Transportation Engineering I, chapter 5, asked 2×
- [Catch water drains in hill roads](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Acatch-water-drain-hill) — Transportation Engineering I, chapter 5, asked 2×
- [Special structures in hill roads](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Ahill-special-structures) — Transportation Engineering I, chapter 5
- [Special considerations in hill road design](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Ahill-special-considerations) — Transportation Engineering I, chapter 5, asked 5×