Where is this sentiment coming from? Let the driver (who is legally, ethically, and morally responsible for the operation of the vehicle they are controlling) judge the appropriate safety boundaries of the environment they're currently driving through. A 45mph zone would be more appropriately driven at anything from 15 to 70mph, depending on so many factors other than "it's off the highway".

At any rate, don't turn a fine piece of engineering that many people have an emotional connection with, not to mention pay a lot of hard-earned money for, into some vaguely-autonomous, ToS-bound appliance that does not what its owner sees fit, but what its maker deems appropriate from medium earth orbit.

Censorship applies to behavior as well as words.