1: https://en.wikipedia.org/wiki/Corporate_average_fuel_economy...
1. Poorer people tend to drive older vehicles, so if you solely encourage higher fuel economies by taxing carbon emissions, then the tax is (at least short-term) regressive.
2. You can work around #1 by applying incentives for manufacturers to make more efficient cars should lead any carbon tax
3. If you just reward companies based on fleet-average fuel economy without regard to vehicle size, then it would be rather bad for US car companies (who employ unionized workers) that historically make larger cars than Asian and European companies.
4. So the first thing done was to have a separate standard for passenger vehicles and light-trucks, but this resulted in minivans and SUVs being made in such a way as to get the light-truck rating
5. We then ended up with the size-based calculation we have today, but the formula is (IMO) overly punitive on small vehicles. Given that the formula was forward looking, it was almost certain to be wrong in one direction or the other, but it hasn't been updated.
Every single one of your ideas has problems that are solved by a carbon tax. Taxes are simple, they accomplish what you want, and they don't have loopholes. A carbon tax will _never_ have the unintended consequence of making emissions worse. Many of our current regulations, including the one I was responding to do exactly that because they actually cause people to buy larger trucks than they otherwise would with worse fuel efficiency.
A carbon tax might not on it's own be enough to solve the problem (especially if you set it to low), but no matter what level you set it, it will help. Thanks to unintended consequences, many of our current regulations are actively counter productive, while _also_ having negative economic and other costs.
"Taxes are simple... and they don't have loopholes" is not at all how taxes work in the US. Perhaps your imagined perfect carbon tax is simple, but a simple tax with no loopholes is not likely to happen. Everyone wants a break or exception, and many of the interested parties are powerful.
You could say the same thing about zoning. Higher density is better for affordability, but faces opposition from landowning existing residents. Does that make it wrong, or not worth pursuing? No, and that particular movement seems to be getting traction despite the political opposition.
I read "trivially fixable" as "there is an elegant solution to this," not that "it is easy to get it politically passed."
> I read "trivially fixable" as "there is an elegant solution to this," not that "it is easy to get it politically passed."
The huge problem with this line of thinking is that it's easy to identify a half-dozen key players standing in the way of your elegant solution and it would be easier to remove them from the situation than change their minds. It's an attractive idea that can become a fixed idea.