Indeed. I believe there is an upper limit of comfort for most people (somewhere in the 80-85 mph) and if the limits were raised to 80mph and then enforced at that using automated methods I would support it.
If we charge companies for polluting, it's reasonable to charge individuals for consuming carbon at an unnecessarily high rate. I'd support automatic fees enforced as drivers hit 65, 75, etc. No limit, per se, just trying to internalize the externalities.
Hard limits are strange for things that are continuous and probabilistic. If we could set an automatic fee equivalent to the cost of increased risks, pollution, etc., it'd be a function of speed. Someday we'll have the technology to communicate that back to the driver as they change speed and location from urban to rural, go through construction zones, etc.
Of course, setting an appropriate gasoline tax, paid at the pump, would reduce the value of those fees.
I suppose the fee would correspond to increased risk, so it'd be cheaper than for someone who was driving a gas guzzler at the same speed. In the ideal (dystopia or utopia?) world, the fee would also take into consideration average rates of collision by vehicle type, perhaps your age, number of hours spent on the road that year, etc.
They're not high enough. And while there are gasoline taxes at the pump, there are various subsidies on the extraction and refining part of the supply chain. I'm not sure the taxes cover the subsidies. It's a wealth transfer from consumers (the ones buying gas) to the producers (the ones receiving subsidy)
