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?

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