What is the grade/slope/angle?

Not that important of a question really. On my way home I get off the road by following a curve around to the right that ends up going over the road I was just on. It doesn’t seem like that steep of a slope, but when I’ve gone all the way around, there I am on the via duct (?) which is about 16 feet higher that the road.
The more I think about the roads and highways, the more ignorant I feel.
Those surveyors and engineers have really got some serious planning to do to make the roads work and come out correctly. It’s actually fairly amazing.
So, how many degrees of an angle is it? Is there a standard angle that they try to stick to or do they adapt to fit the terrain?
These are the things that I think about in the long hours of the night. Sad, huh?