I believe % grade is a measure of the rise to the run or how much the roadway rises compared to the length. If a roadway rose 1' for each 1' of length, that would be 100% grade (or the same as 45°). A 5% grade would rise 1' for each 20' of length or about 2-1/2°. When you are looking into a grade, your perspective is distorted. If you looked at the grade from the side, it would look a lot less imposing.
Disclaimer: There is a good possibility that my explanation is completely bogus, it's just my own understanding or lack of same. /forums/images/graemlins/smirk.gif /forums/images/graemlins/laugh.gif