Hypothetical build questions…

DionR said
"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]

Dude, You haven't got a clue, most people went that fast on every road they could. They did just as they do Today, drive over the limit by at least 5mph, & those inclined a lot more anywhere they figured they'd get away with it.
What are You talking about? The highways are STILL not completed, I remember when some of the local major Interstate links were completed, but stuff like the Mon-Valley expressway started & stopped so many times, street racers used part of it for a while, and a section of overpass sat there stopped in mid-span like a Kenievel jump begging for a taker. Took 2 decades before it got kick-started again. A lot has been completed now, (almost another 2 decades), but it still ain't finished.
Your "gut tells You" what You read on the web, & I don't give a **** who wrote it, the avg American just wasn't, & still isn't afraid of speed. The Interstates were designed for cars of the '50's to "safely travel at 70mph", as most rural 2-lane roads routinely had 50mph speed limits, 70mph & no stoplights or signs were a major improvement. And yes, We know the concern over the ability to move equipment & goods besides relying on the rails after WW2 was the real intial impetus, not Your vacation plans.