Oops! I used those pictures a couple years ago when the issue of max. driveway slope was at issue. Contractors said there was no need to put a max. grade into the code. I showed them the pictures and we settled on 17% with an administrative review for something greater. We were proposing 12%. My own driveway is +20% and occasionally during the winter, I can't get up it. Couple winters ago, a neighbor knocked on my door to tell me my car slid into the street.