---
title: "Superelevation and conditions for providing it"
subject: "Transportation Engineering I"
chapter: 3
key: "semester_6/transportation_engineering_i:super-define-conditions"
source: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/super-define-conditions
site: BCT Engineering
---

# Superelevation and conditions for providing it

Transportation Engineering I · Chapter 3: Geometric Design of Highway

- Asked in: 2062 Jestha (old course), 6 marks
- Video: [What is superelevation in road? How to provide super-elevation in roads ?](https://www.youtube.com/watch?v=G5cUjWHNzGw) — Engr Suliman Khan
- 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-define-conditions
- Whole chapter: https://www.bctengineer.com/md/semester_6/transportation_engineering_i/chapter-3

## Question

What do you mean by super-elevation? Explain briefly in what conditions superelevation can be provided.

## Short answer

Superelevation raises the outer pavement edge on curves to oppose centrifugal force. It is provided when centrifugal ratio exceeds lateral friction (0.15), on curves of small to moderate radius. Design uses e = V²/225R (75% design speed), minimum equals camber, maximum 7% (10% hills). If e exceeds max, use emax and check friction; otherwise increase radius or reduce speed.

## Answer

**Superelevation** is the raising of the outer edge of the carriageway above the inner edge on a horizontal curve, giving the pavement an inward transverse slope. The component of the vehicle's weight down the slope opposes the centrifugal force, so the vehicle can go round the curve safely and comfortably.

$$
e + f = \frac{V^2}{127\,R}
$$

#### Conditions for providing superelevation
1. **When the centrifugal ratio is greater than the lateral friction:** if $v^2/(gR) > f$ (taken as 0.15 for design), friction alone cannot hold the vehicle, so superelevation is needed.
2. **On curves of small to moderate radius** at high speed. On very flat curves (large $R$), the required $e$ may be less than the normal camber; then only a cross slope equal to the camber is provided, with no extra superelevation.
3. **Design value:** $e = V^2/(225R)$ (for 75% of the design speed). If it is less than the camber, a minimum equal to the camber is provided.
4. **Upper limit:** $e_{max} = 7\%$ in plain and rolling terrain and 10% in hilly terrain (IRC), and 7% in snowy or icy areas, to prevent slow or stopped vehicles from sliding down and to limit overturning.
5. **When $e$ comes out more than $e_{max}$,** adopt $e_{max}$ and check that $f = V^2/(127R) - e_{max} \le 0.15$. If not, either increase the radius or reduce the speed limit.
6. In **urban areas** and at junctions, a smaller superelevation (about 4%) is used because of frequent stopping and slow traffic.
7. It must be introduced gradually over the transition length (or tangent) at an allowed rate.

## Check yourself

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

1. Superelevation is needed when
   A. v^2/(gR) is less than f
   B. v^2/(gR) exceeds the available lateral friction (0.15)
   C. the road is straight
   D. the camber is large
   Answer: B. If the centrifugal ratio exceeds f, friction alone cannot hold the vehicle. (Key point: When needed)

2. The design superelevation is based on
   A. full design speed, e = V^2/(127R)
   B. 75% of design speed, e = V^2/(225R)
   C. twice the design speed
   D. the camber only
   Answer: B. e = V^2/(225R) for 75% of the design speed, with minimum equal to camber. (Key point: Design value)

3. The IRC maximum superelevation in plain and rolling terrain is
   A. 10%
   B. 4%
   C. 7%
   D. 15%
   Answer: C. 7% in plain/rolling (10% in hills) to avoid slow vehicles sliding. (Key point: Maximum value)

4. If calculated e exceeds e_max, what is done?
   A. Adopt e_max and check f = V^2/(127R) - e_max <= 0.15; else raise R or lower speed
   B. Ignore superelevation
   C. Increase e above e_max
   D. Remove the curve
   Answer: A. e_max is adopted and the resulting friction is checked; if it exceeds 0.15, increase radius or reduce the speed limit. (Key point: If e exceeds emax)

## Related in Transportation Engineering I

- [Methods of providing superelevation](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Asuper-methods) — Transportation Engineering I, chapter 3, asked 5×
- [Superelevation on 100 m radius curve](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3An-62j-super-100) — Transportation Engineering I, chapter 3
- [Superelevation design for 150 m radius](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3An-79j-super-150) — Transportation Engineering I, chapter 3
- [Raising outer edge for superelevation](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3An-63k-super-raise) — Transportation Engineering I, chapter 3

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- [Spillway need; chute, shaft; ski-jump conditions](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aspillway-chute-shaft-skijump-conditions) — Hydropower Engineering, chapter 4