The EPA has almost nothing to do with fuel economy numbers here are a few facts..
The Corporate Average Fuel Economy (CAFE) are regulations in the United States, first enacted by the U.S. Congress in 1975, in the wake of the Arab Oil Embargo and were intended to improve the average fuel economy of cars and light trucks (trucks, vans and sport utility vehicles) produced for sale in the United States. The Energy Policy and Conservation Act (EPCA), as amended by the 2007 Energy Independence and Security Act (EISA), requires that the U.S. Department of Transportation (DOT) establish standards separately for passenger automobiles (passenger cars) and non-passenger automobiles (light trucks) at the maximum feasible levels in each model year, and requires that DOT enforce compliance with the standards. DOT has delegated these responsibilities to the National Highway Traffic Safety Administration (NHTSA). Through EPCA and EISA, U.S. law (49 U.S. Code § 32919) also requires that "a State or a political subdivision of a State may not adopt or enforce a law or regulation related to fuel economy standards or average fuel economy standards".
You want to really know why FORD and others are trying to increase the average MPG of there fleet with CAFE standards..
In 2006 the rule making for light trucks for model years 2008–2011 included a reform to the structure for CAFE standards for light trucks and gave manufacturers the option for model years 2008-2010 to comply with the reformed standard or to comply with the unreformed standard. The reformed standard was based on the vehicle footprint. The unreformed standard for 2008 was set to be 22.5mpg.
To achieve the target of 35mpg authorized under EISA for the combined fleet of passenger cars and light truck for MY2020, NHTSA is required to continue raising the CAFE standards. In determining a new CAFE standard, NHTSA must assess the environmental impacts of each new standard and the effect of this standard on employment. With the EISA, NHTSA needed to take new analysis including taking a fresh look at the potential impacts under the National Environmental Policy Act (NEPA) and assessing whether or not the impacts are significant within the meaning of NEPA.
NHTSA has to issue its new standards eighteen months before the model year for fleet. According to NHTSA report, in order to achieve this industry wide combined fleet of at least 35mpg, NHTSA must set new standards well in advance of the model year so as to provide the automobile manufacturers with lead time enough to make extensive necessary changes in their automobiles. The EISA also called for a reform where the standards set by the Transportation Department would be are “attribute based” so as to ensure that the safety of vehicles is not compromised for higher standards.
Here is the kicker..
The estimated value of the CAFE exemption gained by Toyota is $2.5 billion; Honda’s benefit is worth $0.8 billion, and Nissan’s benefit is valued at $0.9 billion in reduced CAFE compliance costs. Foreign companies gained $5.5 billion in benefits compared with the $1.8 billion that went to the Detroit Three.
So the answer is Government subsidies and how much uncle sam is going to pay them for getting better fuel economy in the fleet of cars and trucks it sells...
The EPA is just not involved in this surprisingly..