The steepness of the slope is irrelevant once you're on it - it's the transition between grades at the intersection of the drive & street that is critical. I have a steep drive with an abrupt transition that is exacerbated by a drainage gutter at the intercept. On top of that the street is actually on another down-grade perpendicular to my driveway!
However, even though my car is lowered, I can accommodate it by cutting the angle at 45 deg as I transition across the intercept. If I was coming from the downhill side of the street though, forget it!
If you are designing a driveway from scratch make it flatter at the bottom (at the street intersection) then gradually transitioning somewhat exponentially to the final grade, as opposed to a fixed linear slope at a fixed angle to the street. Think of the drive as a series of small angular changes rather than a single abrupt one. The greater the distance between these changes in angle the easier it will be.