The law requiring cars to meet these fuel efficiency tests was written in the 1970s, and specifically sets standards based on the technology then. Worse,
[T]he EPA doesn’t know exactly how its CAFE testing correlates with actual results, because it has never done a comprehensive study of real-world fuel economy. Nor does anyone else. The best available data comes from consumers who report it to the DOT—hardly a scientific sampling.
Other than that, everything is fine. Companies are forced to spend billions on this regulation, the costs of which they immediately pass on to consumers, all based on fantasy and a badly-written law. Gee, I’m sure glad we never tried this with healthcare!