When congress repealed the federal speed limit, Montana did apparently post their speed limit as “Safe and prudent,” though trucks were limited to 60 or so. Later, according to my guidebook, this was struck down by the Supreme Court as being too vague. So, now the interstate in Montana has a 75 mph speed limit, and US-2, which I took, is limited to 70 mph (though, 65 mph at night… while I agree that their long empty stretches of road are more dangerous at night, when wildlife could appear out of nowhere, will the 5 miles an hour really make a difference?). On the other hand, I didn’t see a police car on US-2 at all, so maybe enforcement isn’t common.