---
title: "Short note: hairpin bends"
subject: "Transportation Engineering I"
chapter: 5
key: "semester_6/transportation_engineering_i:hairpin-bend"
source: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/hairpin-bend
site: BCT Engineering
---

# Short note: hairpin bends

Transportation Engineering I · Chapter 5: Hill Roads

- Asked in: 2068 Magh (old course), 4 marks; 2065 Kartik (old course), 4 marks; 2063 Kartik (old course), 4 marks; 2062 Jestha (old course), 4 marks (asked 4 times)
- Video: [Hairpin bends requirements and design, How to provide a hairpin bend on hill road, IRC 52 and IRC 73](https://www.youtube.com/watch?v=pmrdcfGoau4) — Transportation Engg Talks | Satish IITR
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/hairpin-bend
- Whole chapter: https://www.bctengineer.com/md/semester_6/transportation_engineering_i/chapter-5

## Question

Write a short note on hair pin bends.

## Short answer

A hairpin bend is a sharp U-turn (deflection >120°) on hill roads to gain height in steep terrain. It should be on stable ground with minimum inner radius 14 m, gradient ≤2.5 %, superelevation up to 10 % and at least 60 m between consecutive bends.

## Answer

A **hairpin bend** is a sharp turn of about 180 degrees (deflection angle larger than about 120 degrees) that is introduced on a hill road to gain height when the natural ground slope is too steep for the road to climb within the ruling gradient. The road doubles back on itself in a "U" shape on a spur or gentle spot.

#### Types
- **Circular type** - one circular arc of radius R with straight approaches.
- **Compound/Transition type** - a central circular arc with two transition curves; used for larger radii and where the road is wide.
- **Symmetrical** and **unsymmetrical** hairpins, depending on the layout around the apex.

#### Design and location (IRC:SP:48; NRS 2070 follows similar limits)
- Locate on a stable, gentle (preferably < 30 degrees) and well-drained hill slope, on a spur or bench, never on a landslide-prone or unstable slope; avoid cutting a deep slice.
- Minimum radius of the inner curve about 14 m (IRC). Extra widening is provided on the inner side so that vehicles can turn.
- Gradient on the curve: not steeper than 1 in 40 (2.5%) on the hairpin (and not flatter than 1 in 200 for drainage); approaches within the ruling gradient (about 5-6%).
- Superelevation up to 10% (1 in 10) maximum; the full superelevation is achieved by rotating about the inner edge.
- A minimum intermediate distance of 60 m between consecutive hairpins (and between a hairpin and other curves) where possible.
- Provide good drainage, retaining/breast walls and parapets, adequate sight distance, and an adequate roadway width at the bend (IRC: about 9.0 m for single-lane and 11.5 m for double-lane roads, including widening).
- Avoid more than a few hairpins in a series; if they are needed, space them well apart.

Hairpins increase the road length, construction cost and vehicle running cost, so they should be used only when developing length by switchbacks cannot be avoided.

## Check yourself

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

1. Why is a hairpin bend introduced on a hill road?
   A. To shorten the road
   B. To gain height when the natural slope is too steep to climb within the ruling gradient
   C. To increase design speed
   D. To avoid any curve widening
   Answer: B. The road doubles back (about 180 degrees) to develop length and gain height at an acceptable gradient. (Key point: Purpose of hairpin)

2. Where should a hairpin bend be located?
   A. On a landslide-prone slope
   B. In a deep slice cut
   C. On a stable, gentle, well-drained slope such as a spur or bench
   D. On a waterlogged slope
   Answer: C. A stable, gentle and drained site, preferably under 30 degrees, avoids slides and deep cutting. (Key point: Location)

3. Which design limit applies to hairpin bends?
   A. Gradient on the curve not steeper than 1 in 40 (2.5%) and minimum inner radius about 14 m
   B. Gradient of 10% on the curve
   C. Radius of 5 m
   D. No widening required
   Answer: A. The gradient on the curve is limited to 1 in 40, the radius is about 14 m (IRC), and curves are widened with a 60 m straight between hairpins. (Key point: Design limits)

## Related in Transportation Engineering I

- [Hair pin bend elements](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Ahairpin-elements-derive) — Transportation Engineering I, chapter 5