Grade and Slope
Grade and slope (or angle) are not the same thing. The graphic above illustrates how a 90-degree angle is infinite. Typical U.S. interstates and major highways are capped at an 8 percent grade. This is a 4.57 percent slope. When you compare this to a protractor it barely registers. Much different than your driving experiences in the mountains. And nowhere near the road sign depiction of a 50 percent grade.