A super-elevation $e$ is provided on a circular horizontal curve such that a vehicle can be stopped on the curve without sliding. Assuming a design speed $v$ and maximum coefficient of side friction $f_{max}$, which one of the following criteria should be satisfied?

- $e \leq f_{max}$
- $e > f_{max}$
- no limit on $e$ can be set
- $e = \dfrac{1-(f_{max})^2}{f_{max}}$