They should just "freeze" the emissions standards to EPA Tier 2 Bin 5 for automobiles--already achievable now at a reasonable price, especially with the extremely precise control of the fuel ignition process. In fact, the exhaust coming out of a Tier 2 Bin 5 certified engine is often cleaner than the air going into the engine!
Secondly, diesel-electric locomotives should all be certified to standard slightly better than the Tier II standard, which already removed just about all the harmful emissions from diesel prime movers anyway, especially particulates and NOx gases.
Between the CAFE standards and the EPA standards, it is a wonder that we even have cars that we want to drive.
Behold the power of research + time.
I wonder how small the EPA would become if the federal gov’t froze all existing standards in place?