Average fuel economy for cars and light trucks decreases 12% going from 50 to 60 MPH: https://www.energy.gov/eere/vehicles/fact-982-june-19-2017-s...
Heavy trucks are the exception, they are typically designed for an operating point of 65 MPH. However, there are huge losses above that speed. No reason for a heavy truck to be going 70 or 75 MPH.
The American Trucking Association actually endorses a nation 65 MPH speed limit for trucks, which they say would save 280 million gallons of diesel per year: https://www.fleetowner.com/emissions-efficiency/article/2166...
I'm always amazed in the midwest what a difference there is between traffic in states that have (and actually enforce!) a "get out of the left lane" law vs states that don't.
I-80 across the eastern half of Iowa in particular is exhausting to drive on, because a lot of people camp in the left lane and clog up traffic. That leads to desperate and aggressive driving to get around these silly bottlenecks, which kills fuel efficiency and makes the roads more dangerous.
Those laws are unAmerican: they're about people doing what's best for the common good, instead of being selfish, and that's completely contrary to American ethics and mindset. That's why Americans generally hate those "keep right except to pass" signs and ignore them.
We will then eliminate all old cars by raising taxes on them beyound what any sane person would pay.
It’s coming. Total control.