"On January 2, 1974, President
Richard M. Nixon signs the Emergency Highway Energy Conservation Act, setting a new national maximum speed limit."
[URL]https://www.history.com/this-day-in-history/nixon-signs-national-speed-limit-into-law[/URL]
Found one comment that Congress enacted a national 55mph speed limit in '72. Not sure what the difference was.
Later than I thought, no idea if or what the speed limits was before then. But not '77 either.
Just my gut, but I have doubts that people regularly traveled at 65-70 mph prior to the 55 speed limit. But just a guess.
Besides, the world was different then and the highways weren't even completed.
[URL]https://www.roadandtrack.com/car-culture/classic-cars/a26254/regular-car-reviews-ford-falcon/[/URL]