The speed limit is a balancing act, too fast and you use significantly more fuel overall.

Too slow and your roads will be too crowded, if the same numebr of cars are on the road overall.

10 hours at 70=700 miles
10 hours at 55=550 miles

That leaves the same car on the road 70/55 longer which adds up to more congestion which will cause more problems in a snowball effect.

The optimal speed should be where the most cars get the best mileage probably 55-60. This is considering the congestion effect as an equal factor.

Anither consideration would be where the trucks get the best mileage.

regards
gary

let's make burning fossil fuels a felony!

You're overlooking the fact that there's an effect in the other direction. At lower speeds, stopping distances are reduced, which means the cars can be closer together. So at a given moment, a given mile of highway can have more cars on it, before being filled to capacity.

If you viewed the road from above, you would see more metal and less pavement. The line of cars would look more and more like a train.

And less overall wind resistance.

Good point, I didn't think of that. Overall efficiency would improve because vehicles closer together would tend to create more of a drafting effect.

Nah most people are stupid...

and those people who you say can "buy" family time by speeding would rather be at work than at home earning more money to keep up their lifestyles. That and they would buy maybe minute of saved time by speeding...

People around here are still not going much faster than 55 on 55mph highways. Im going about 50-55 and sure Im getting past but their not whizzing by like they used to. Still get the uppity douche bags in the 4 ton SUV's and crappy driving soccer moms but they usually get boxed in so they cant go much more than 55 lol

When cars are closer together, the "accordion" effect becomes more pronounced. Speed up, then slow down to a crawl or even a complete stop.

From what I understand, the mathematics of this are very complex and not at all well understood. I do know from my own observations that the closer together the cars are on the highway, the more likely this is to happen..

The "accordion" effect is extremely inefficient and fuel could be saved by higher speed travel that does not vary a great deal.

10% increase in average speed on a 100 minute daily commute would be 10 minutes bought. 20mph over 55 (75 being a common speed for speeders on 55mph highways) is about 40% over, and covers for time spent at traffic lights that can't go any faster, easily making a 10% increase in average speed. My commute is a little more than 100 minutes daily. Those are more realistic numbers than "maybe [one] minute".

Interesting reading on this:
https://www.eskimo.com/~billb/amateur.../traffic1.html

"Interesting reading"

Excellent link, thanks.

I read that a while back, it is indeed interesting.