Which should make the "solution" obvious to the regulators. To license them as a "passenger car", they have to also meet passenger car safety, emissions, and f

Which should make the "solution" obvious to the regulators. To license them as a "passenger car", they have to also meet passenger car safety, emissions, and fuel economy standards. If they don't meet those standards (that were in effect as of their build date) then they can't be licensed as a "passenger car".