Superelevation Calculator
A 300 m radius curve designed for 80 km/h gets the maximum superelevation, 7 %, and then needs a lateral friction of 0.098, within the IRC limit of 0.15.
IRC: 7 % on plain and rolling terrain, 10 % on hill roads not snow-bound.
IRC: 0.15.
7 %
- e for 75 % of speed, no friction: V²/225R
- 9.481481481 %
- Friction needed at full speed
- 0.09797900262
- Check
- f = 0.09798 ≤ 0.15: OK
- Ruling minimum radius V²/127(e + f)
- 229.0622763 m
Step-by-step solution
- e = V²/(225R) = 80² ÷ (225 × 300) = 0.09481481481 > 0.07, so e = 0.07
- f = V²/(127R) − e = 0.1679790026 − 0.07 = 0.09797900262
Superelevation Formula
e + f = V² / (127R)
IRC design: e = V²/(225R) ≤ e max (7 %), f ≤ 0.15
Worked Example
A 300 m curve designed for 80 km/h:
- e = V²/(225R) = 80² ÷ (225 × 300) = 0.09481481481 > 0.07, so e = 0.07
- f = V²/(127R) − e = 0.1679790026 − 0.07 = 0.09797900262
Friction needed at full speed: 0.09797900262 · Check: f = 0.09798 ≤ 0.15: OK · Ruling minimum radius V²/127(e + f): 229.0622763 m
GATE tip
Follow the IRC sequence: e for 75 % speed, cap at e max, then check f at full speed, then restrict speed if needed.
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Frequently asked questions
Why does IRC use 225 instead of 127?
It provides superelevation for 75 % of the design speed with no friction: (0.75V)²/127R ≈ V²/225R.
What if friction exceeds 0.15?
The curve cannot be negotiated safely at the design speed; the speed must be restricted to √(127R(e + f)).
Sources
- The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures .
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
Cite this page
APA
Scientific Converters. (2026, October 15). Superelevation Calculator. Retrieved October 29, 2026, from https://scientificconverters.com/calculators/superelevation-calculator/
IEEE
Scientific Converters, "Superelevation Calculator," scientificconverters.com. Accessed: Oct. 29, 2026. [Online]. Available: https://scientificconverters.com/calculators/superelevation-calculator/