They did away with that a long time ago.When I was learning to drive they always told me Montana had no speed limits through most of the state.
My buddy that lived they're said it was a "drive at a safe and reasonable speed" type of thing
Guess I got bad info.
**** edit this was over 20 years ago.
Most highways are 75mph, 80 in some spots.
I'm sure they lost out on a lot of revenue with the "no speed limit" stuff.
ETA: My profile might be misleading, I live in WA right now. I own property in MT and am doing everything I can to get relocated to the USA again.