This week the EPA filed a Final Rule that stops states from setting their own fuel efficiency fleet standards. California and 13 other states have more slightly aggressive fuel efficiency standards than the current EPA standards (AZ does not). If today’ final rule withstands certain challenges it'll prevent those states from having enhanced standards.
That's important because the EPA is about to roll back the current federal fleet emission standards. More on that in a bit.
Under the existing national regulations, new cars, trucks, and SUVs fleets need to average about 50 miles per gallon by 2025. But back in 2018 the EPA & NHTSA proposed a roll back of the existing national vehicle fleet fuel efficiency standards (the current CA standard is basically the same as the current federal standard).
If the CA standard and the current national standard are the same, then what's the big deal?
It's a big deal because the Administration has proposed (but not yet finalized) a Rule that will roll back the current standards by stopping the progression of standards in 2021. Rather than requiring a fleet average of 50 mpg by 2025, the proposed new federal standard would stop at 38 mpg (last year, the average fleet fuel efficiency was about 25 mpg),
So basically, the EPA this week set the stage for preventing CA and 13 other states from keeping the current standard of 50 mpg by 2025 when the EPA officially rolls back the standard (probably in the coming weeks).
Fuel efficiency standards are an important driver that pushes vehicle manufacturers to discover new ways of improving fuel efficiency and are an important strategy toward reducing greenhouse gas emissions. The transportation sector is the largest contributor to atmospheric CO2 emissions.