# formula for super elevation

I'm practicing some questions for my upcoming exam and I need the formula for super elevation when you've been given the coefficient of lateral friction in the question

## 2 Answers

The equation for highway superelevation is

$$e + f = \dfrac{V^2}{gR}$$

where:

• $$e$$ is the rate of superelevation in %,
• $$f$$, the friction coefficient of the pavement,
• $$V$$, the velocity,
• $$g$$, the gravitational acceleration,
• $$R$$, the radius of the curve.
• it's more complicated. it has to do with local climate, the posted speed, frequency of intersections, state and federal codes. – kamran Mar 1 at 3:14
• @kamran is the OP in the US? – Solar Mike Mar 1 at 6:47
• @Solar Mike, i don't know. but i suspect no county will allow a stalled bus on a frozen highway bend slide down and cause a catastrophic traffic jam. – kamran Mar 1 at 6:55
• @kamran our buses carry wedges for that sort of eventuality. But if the conditions are right (wrong) just a gentle slope allows vehicles to slide without engine power... – Solar Mike Mar 1 at 6:59
• I think the OP is preparing an upcoming examination administered by the department of engineering, not the school of urban planning. – r13 Mar 1 at 16:28

Here is the formula to calculate Superelevation.

e + f = V*2 / 127R

where

e = Rate of Superelevation in %

f = Lateral Friction Factor

V = Velocity of the Vehicle in m/s

R = Radius of Circular Curve in Meters • Welcome to Engineering! I've given this answer a -1 because it doesn't seem to add any information when compared to the existing answer by @r13. In fact, it's apparently a specific case only applicable when using the metric system. – Wasabi Mar 2 at 11:41
• @Wasabi what’s wrong with metric units? Surely if the units are consistent then it works. – Solar Mike Mar 2 at 12:25
• @SolarMike: Absolutely nothing. I've used SI my entire life (I'm Brazilian, not American or from other former British colonies, so only ever use imperial units when designing pipes which for some reason are in inches even here), and have very strong feelings about its superiority to imperial which I'll keep to myself. However, this answer just seems to be Pareto-dominated by r13's. – Wasabi Mar 2 at 12:48