Technology

To be even fairer, having such overly-strict emissions standards for diesels was a bad idea to begin with. Destroying diesels and forcing everyone into gasoline cars instead saved a little bit of pollutants like soot, NOx, and SOx, sure, but came at the expense of much lower efficiency/higher greenhouse gas emissions.

The worst part is that biodiesel burns much cleaner than dino-diesel, but isn't compatible with the fancy injection systems and emissions equipment on "clean diesel" engines. If we had let them keep building the same circa-2000 engine tech, we could've cleaned up the whole fleet at once simply by switching out the fuel (while still keeping the same high efficiency and reducing GHG emissions to net-zero because biodiesel is part of the short-term carbon cycle instead of the long-term one), but now we can't because all the new engines (at least, the few remaining on the market in trucks but not small cars) break if you use more than 10% or so biodiesel in them.