The answer is right in the text of your question: the 85% rule of thumb is for highways. If it makes you feel better I've seen a proposal to offer a discount on

The answer is right in the text of your question: the 85% rule of thumb is for highways. If it makes you feel better I've seen a proposal to offer a discount on speeding tickets in Texas if you pay with bitcoin. No, actually, I made that up. It's funny because it's so very plausible.