55 wasn’t a federal mandate. They couldn’t mandate to the states. What they did do, instead was,
threaten to withhold road funds if the state didn’t lower their speed limit to 55.
It was in response to the 1973 oil crises. Nixon signed it into law.
I think a couple a states told the feds to take a hike.
A ticket in Montana was $2 and you couldn’t be issued one more than once a day…