I don't think that is quite right. From Wikipedia:
On March 10, 1996, a Montana Patrolman issued a speed ticket to a driver traveling at 85 mph (140 km/h) on a lonely stretch of State Highway 200. The 50-year-old male driver was operating a 1996 Camaro with less than 10,000 miles (16,000 km) on the odometer. Although the officer gave no opinion as to what would have been a reasonable speed, the driver was convicted. The driver appealed all the way to the Montana Supreme Court. The Court reversed the conviction in case No. 97-486 on 23 December 1998; it held that a law requiring drivers to drive at a non-numerical "reasonable and proper" speed "is so vague that it violates the Due Process Clause ... of the Montana Constitution". Due to this reversal, Montana scrambled to vote in a numerical limit as it technically had no speed limit whatsoever in the meantime. In June 1999, a new Montana speed limit law went into effect. The law's practical effect was to require posted limits on all roads and disallow any speed limit higher than 75 mph (120 km/h).
The decision is posted here: http://caselaw.lp.findlaw.com/scripts/getcase.pl?court=MT&vol=97&invol=486
I was just relating the story as I had heard it from some friends in Montana, and should have qualified it as such.
BTW, highway 200 goes through West Jordan...Winnett...and except for Circle and Sidney, it is all a lonely stretch of highway.
They do not call this part of Montana "The Big Empty" for no reason. I am about 2 miles from Highway 200 now, working on an oil drilling location.
Thanks to you both for the information. I was wondering why a police cruiser pulled over to get out of my way on my one trip thru Montana. I was going about 90, and when I realized it was a police car I really panicked. Now it all makes sense....