What is the maximum vehicular slope?

Okay, so, maximum vehicle slope, right? It's 1:15, or about 6.67%. Think of it this way: for every foot the ground goes up, you need 15 feet of ramp. Makes sense, yeah? I mean, imagine trying to drive up something steeper! My grandma's driveway is pretty steep, maybe close to that limit, and even that can be a little hairy in the winter. I remember one time, icy conditions, almost slid right back down! Anyway, anything steeper than 1:15, forget it. No way you're getting a permit for that for parking or, you know, actually getting around in your car. They're just not safe. I think I read somewhere they tested this extensively – probably with dummies in cars, I bet! – and that’s the safest practical limit. So, 1:15 it is.