Seems like we could help things a lot by adding this regulation to trucks in America. Slower == better fuel efficiency and safer too!
If you're looking for levers to tweak the system, this probably ain't the one.
Drivers are paid by the mile, if you drive faster your effective hourly pay goes up.
It's more complicated than that. Up to highway speeds, energy costs are dominated by mechanical losses like rolling resistance. Meanwhile engine efficiency is higher at particular engine speeds and power outputs, and higher gearing improves efficiency but only if the engine remains in its optimal efficiency range.
This implies there is an optimal speed before aerodynamic losses become dominant, but that speed increases based on various factors like the air viscosity and vehicle aerodynamics. So the optimal speed will be higher at higher altitudes (common in the western US) and higher for vehicles with better aerodynamics.
> Drivers are paid by the mile, if you drive faster your effective hourly pay goes up.
This is another type of efficiency. It does you little good to reduce your fuel costs by $100 if you increase your labor costs by $200.
The only type of road where a regulator would make sense is the kind of road where in the US a regulator makes no sense. Every other type of road already has speed limits at or below what a regulator would be set to.
(Bearing in mind that US highways are radically different from Europe's)
What I am familiar with is lots of curves, inclines, declines. The kind of road where a loaded truck going the limit easily flips into the cliff to the side on the slightest error.
US highways are (by design) very straight, very flat, and very long. And on the rare occasion they're not, there are already speed limits in place.
(It's not an exaggeration because there seem to be about 2 state patrol cars and they're always parked at Walmart getting coffee. If you want to drive 100 as private passenger vehicle, go right ahead. If you want to drive 85 with a rig full of cows, feel free. While Nevada and Montana lost their no speed limit statuses due to federal funding and regulations, but worked around it by issuing smaller penalties.)