The other thing that makes hill grade percentage calculations all wrong is that a hill may be .5 mile long at a calculated 6% but if say it has a 10 or 12%
section within that number it is a lot tougher climb. I always wondered why I had so much trouble with a short hill in our area until I discovered the middle part of it is 14%! even though the whole thing is less than 10% when you do the math. The road would be illegal to build today according to our township manager.