In fact, the reason most national highways have a speedlimit of 50mph, even out in the boonies in Kansas where everything is flat and straight, is because of the fuel crisis of the 70s.
When I was a child, I was curious why highways were 50mph but the interstates had a speedlimit of 65-70mph, so I went and found out instead of assuming it was a disingenous revenue grab.
Most interstates were generally built after the fuel crisis, and they modified the national speed limit in 1988, setting the speed to 65mph, again for efficiency reasons. It was repealed in 1995. Perhaps 65mph is what was considered safe for the road and vehicular technology at the time, and no one has had the political or municipal capital to do a new study ever since.
You want that speed limit changed, contact your reps, I guess.
Wouldn't this be an argument for a higher EV speed limit?
The efficiency loss at speed still applies to EVs due to friction and laws of momentum.