President Barack Obama announced an agreement with 13 automakers in July to strengthen pollution and fuel-efficiency standards that would require all new cars and light trucks to deliver 54.5 miles per gallon (mpg) by 2025. But these new standards would not have been possible had California not passed a 2002 law that tightened its own vehicle greenhouse gas emissions standards, which had the effect of raising fuel efficiency for cars sold in the state. Thirteen other states had followed suit by 2007, giving the president the political leverage to push for more stringent federal rules.

"Everything you see today can be traced back to what NRDC and California accomplished in 2002," says Roland Hwang, NRDC's transportation program director, adding that NRDC co-sponsored California's legislation and later lobbied on Capitol Hill to garner support for tougher federal standards.

The federal government strengthened car and light truck pollution and fuel-economy standards in 2009 to require a 35.5 mpg average for the 2016 model year. NRDC estimates that the tougher standards will cut U.S. oil consumption by about 1.5 million barrels per day by 2030, almost as much as the country imports from the Persian Gulf. The tightened standards will also generate about $80 billion in consumer fuel savings by 2030.

The federal government and the California Air Resources Board -- which earned a seat at the table for its role in pioneering improved standards -- will review automakers' progress in 2018.