However, in recent years, as oil prices have spiked to historic levels, and concerns over greenhouse gas emissions and climate change have grown, there has been a resurgence in interest in the fuel economy and emissions of motor vehicles in the United States. Proponents of higher vehicle fuel efficiency standards argue that they create incentives for the development of new technologies that will help reduce dependence on imported oil and better enable the United States to use scarce resources and limit greenhouse gas emissions—technologies that would not be developed in the absence of that "technology push." Critics argue that efficiency standards distort the market for new vehicles, compromising consumer choice, and that other policy mechanisms (e.g., higher fuel taxes) would be more effective at reducing petroleum consumption and emissions. Fuel consumption and greenhouse gas (GHG) emissions from motor vehicles are closely linked. For these reasons, the Obama Administration has issued joint rules on vehicle fuel economy and GHG emissions for model year (MY) 2012-2016 passenger cars and light trucks, MY2014-MY2018 medium- and heavy-duty trucks, and MY2017-MY2025 passenger cars and light trucks. Passenger Vehicle Standards for MY2017-MY2025

On August 28, 2012, the Obama Administration issued final rules to tighten passenger vehicle fuel economy and greenhouse gas (GHG) standards for MY2017-2025. In a similar process to the landmark agreement that led to new fuel economy and greenhouse gas standards for MY2012-MY2016, the Administration has secured commitment letters from the state of California and from 13 automakers. Many stakeholders were concerned about a potential "patchwork" of different federal and state standards if EPA, NHTSA, and California were to establish different standards at the intersection of fuel economy and GHG emissions. Two key parts of the agreement are that California will treat any vehicle meeting the new federal GHG standards as meeting California standards, and that the automakers agree to not challenge the new standards in court. The Administration expects that consumers' fuel savings from the new standards will more than offset the additional cost of the new technology for these vehicles, which could be thousands of dollars per vehicle. EPA and NHTSA expect that the new standards will save roughly 4 billion barrels of oil and 2 billion metric tons of greenhouse gases over the life of the vehicles covered under the new standards. Critics have challenged the Administration's assumptions, countering that the costs will be higher and could lead to a drop in new vehicle sales. The Energy Policy and Conservation Act of 1975 (EPCA) requires NHTSA to set Corporate Average Fuel Economy (CAFE) standards for passenger cars and light trucks. The oft-cited "standard" of 54.5 mpg in MY2025 for the rule is a proxy for the actual GHG standard of 163 grams per mile (g/mi) of carbon dioxide (CO 2 ) equivalent. As the vast majority of vehicle GHG emissions come from fuel combustion, the primary means for achieving the standards will be through fuel economy increases.
In recent years, as oil and gasoline prices have risen and concerns over greenhouse gas emissions and climate change have grown, there has been a resurgence of interest in the fuel economy and emissions of motor vehicles in the United States. Federal fuel economy and greenhouse gas standards have become a focal point for addressing these concerns. The debate over rising fuel efficiency and greenhouse gas standards for passenger vehicles and heavy trucks has been controversial. Proponents of higher fuel economy argue that new standards will create incentives for the development of new technologies that will help reduce oil consumption and limit greenhouse gas emissions. Critics argue that these standards will impose regulatory costs which will distort the market for new vehicles, and that other policy mechanisms would be more effective at reducing petroleum consumption and emissions (e.g., higher fuel taxes).
On August 28, 2012, the Obama Administration issued new passenger vehicle fuel economy and greenhouse gas standards for vehicle model years (MY) 2017-2025. The National Highway Traffic Safety Administration (NHTSA) and the Environmental Protection Agency (EPA) expect that combined new passenger car and light truck Corporate Average Fuel Economy (CAFE) standards will rise to as much as 41.0 miles per gallon (mpg) in MY2021 and 49.7 mpg in MY2025, up from 34.1 mpg in MY2016. To the extent possible, new CAFE standards will be integrated with federal and state greenhouse gas (GHG) standards for automobiles, because fuel economy improvements are a key strategy for reducing vehicle emissions. If all of the GHG reductions were made through fuel economy improvements, the equivalent miles-per-gallon requirement would be 54.5 mpg in MY2025. However, other strategies will also be used (for example, improved vehicle air conditioners) to reduce GHG emissions to the actual GHG standard of 163 grams of carbon dioxide per mile.
The Administration expects that consumers' fuel savings from the new standards will more than offset the additional cost of the new technology for these vehicles, which could be thousands of dollars per vehicle. EPA and NHTSA expect that the new standards will save roughly 4 billion barrels of oil and 2 billion metric tons of greenhouse gases over the life of the vehicles covered under the proposal. Critics dispute some of the Administration's assumptions. They counter that the costs will be higher and could lead to a drop in new vehicle sales, as the higher vehicle costs may put new car financing out of reach for many consumers.
In a similar process to an earlier Obama Administration agreement that led to new fuel economy and greenhouse gas standards for MY2012-MY2016, the Administration has secured commitment letters from the state of California and from 13 automakers to support the MY2017-2025 rulemaking as well. There has been concern about a potential "patchwork" of different federal and state standards if EPA, NHTSA, and California were to establish different standards on fuel economy and GHG emissions. Two key parts of the agreement are that California will treat any vehicle meeting the new federal GHG standards as meeting California standards, and that the automakers agree to not challenge the new standards in court.
In August 2011, the Administration also tightened fuel economy and GHG emissions standards for MY2014-MY2018 medium- and heavy-duty trucks.