As reported by Automotive News, there are several areas where automotive manufacturers can gain credits. The first is for pure electric, fuel-cell and plug-in vehicles. Starting in 2017, for example, EVs and fuel-cell cars would be counted as two vehicles with zero emissions, with a gradual phase down to 1.5 in 2021. Plug-ins would go from 1.6 to 1.3 in the same time period. Next, full-sized pickups would get a credit of between 10 and 20 grams of CO2 per mile for employing a mild to strong hybrid setup. Third, using more advanced air-conditioners and refrigerants that reduce hydrofluorocarbon emissions could result in a 18.8 to 24.4 grams per mile credit for cars and trucks, respectively. Finally, using advanced technologies like active grille shutters, high-efficiency alternators and lights, and start-stop among others would get credits of between less than one gram per mile to five grams per mile for each vehicle.
We have no doubt automakers will be using these credits to, in essence, "game the system" into getting lower CO2 emissions (and hence fuel economy) than what the vehicles actually produce. It's not that these technologies don't improve fuel economy – they do – just not as much as a 54.5 mpg standard makes it sound.