It's not certain what if anything the White House can do next, although EPA chief Scott Pruitt has been pushing to relax the standards and reduce the ability of states to set stricter environmental protection policies. Companies could still be on the hook if they fell short of goals, but the chances of their falling short would be that much lower.

As it stands, the administration's attempt to roll back penalties may have come too late for both hesitant automakers and the fossil fuel industry. Many major car companies are ramping up their electric vehicle efforts to the point where they'll have many EV models on the road within the next few years. Average efficiency is likely to climb simply because fewer cars will be using fuel in the first place, and a gas-guzzling SUV may soon become more of a liability than an asset.