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CENTER for BIOLOGICAL DIVERSITY Because life is good

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Because of its near-total dependence on petroleum fuels, the U.S. transportation sector is responsible for about a third of our country’s climate-changing emissions. Globally, about 15 percent of manmade carbon dioxide comes from cars, trucks, airplanes, ships and other vehicles.

Reducing transportation emissions is one of the most vital steps in fighting global warming — and solutions to the transportation problem are already available. Our nation needs to shift away from fossil fuel-powered vehicle dependence and the suburban sprawl that accompanies it — and toward alternative fuels, alternative and public transportation, and better land-use patterns to begin reducing our country’s total vehicle miles traveled each year. The Center is working on all aspects of the transportation problem, from advocating for increased fuel economy standards to challenging new sprawl developments, using existing laws and working for new regulations to restrict vehicle emissions and take advantage of alternative-fuels technology for the benefit of the planet.


Cars, trucks and sport utility vehicles driven by U.S. citizens are to blame for about two-thirds of greenhouse gas emissions from the U.S. transportation sector. As more passenger vehicles hit the roads, this pollution will increase dramatically unless strict emissions-reduction and fuel economy policies are in place.

We have a long history of working for stronger regulation of both greenhouse pollution from automobiles through the Clean Air Act and higher fuel economy standards pursuant to the Energy Policy and Conservation Act, two partially overlapping and complimentary statutory schemes. As a member of the large plaintiff group in Massachusetts v. EPA, we celebrated the Supreme Court’s April 2007 decision declaring CO2 a pollutant under the Clean Air Act and ordering the Environmental Protection Agency to take the next step toward regulation by making what’s called the “endangerment finding” — an agency determination that a pollutant “endangers public health and welfare,” leading directly to controls on that pollutant. Despite the Supreme Court’s decision, the Bush administration managed through a series of stall tactics to put off any regulation of CO2 from automobiles until the next administration. In September 2009, the Obama administration announced the first national plan to regulate greenhouse gases under the Clean Air Act for cars, light trucks and SUVs, and in December the EPA finally made it official that greenhouse gas emissions from cars and other sources endanger public health and welfare.

We successfully challenged the Bush administration’s refusal to let California implement its own, stricter-than-national tailpipe emissions limits under the Clean Air Act, and in June 2009 the EPA issued a waiver to let California enforce its own automobile emissions rules, which also allowed a dozen other states to enforce the same rules.
Fuel economy standards for automobiles, set by the Department of Transportation pursuant to the Energy Policy and Conservation Act, also impact the amount of CO2 emitted by vehicles. After major advances in the late 1970s, fuel economy stagnated and even regressed for several decades, despite the law’s mandate to set fuel economy standards at the “maximum feasible level.” The Center won a major lawsuit against the Department of Transportation for failing to properly account for greenhouse gas emissions when it set unreasonably low national fuel economy standards for pickup trucks and sport utility vehicles. In December 2007, Congress mandated an increase in fuel economy to 35 miles per gallon for all passenger vehicles by 2020. In September 2009, the Department of Transportation and Environmental Protection Agency proposed a rule to increase national gas-mileage standards for cars, trucks and SUVs by about 5 percent per year.

After President Barack Obama took office, the administration surprisingly announced that its own fuel-economy standards would be about a mile per gallon lower than Bush’s. Less than a week later, the Center filed suit to overturn them, and in 2010 the administration announced its intent to increase fuel economy standards, with the most ambitious proposal raising them to about 37 miles per gallon by 2017.

In August 2012, standards were finalized that mandated reaching maximum gas mileage of 54.5 miles per gallon by 2025. But once various credits and “flexibilities” are accounted for, the estimated mileage drops to about 47 miles per gallon. Cars are commercially available today that meet and exceed this standard. 

Regarding fuel-economy standards, there have been changes for the better, but they're not good enough. The technologies currently exist to dramatically increase our fuel efficiency today to as high as 45 miles per gallon — and we must take advantage of these technologies in order to reduce atmospheric greenhouse gas concentrations to 350 parts per million and prevent climate catastrophe. We urgently need to transition to hybrid, plug-in hybrid and electric vehicles powered by renewable energy.


Cars aren’t the only vehicles that pollute — airplanes and marine vessels produce a large portion of the world’s greenhouse gas emissions, and this contribution can only be expected to increase. Aircraft not only emit 12 percent of CO2 emissions from U.S. transportation sources — they also emit nitrogen oxides other than nitrous oxide, causing warming when emitted at high elevation. And ships, besides releasing almost 3 percent of the world’s CO2 (about as much as all of Canada emits), are also a main source of nitrous oxide and black carbon (soot).

In July 2008, after the Bush administration refused to respond to our 2007 petitions to reduce emissions from planes and ships, the Center joined a coalition of conservation groups and state attorneys in filing a notice of intent to sue unless the Environmental Protection Agency addresses global warming pollution from these sources.


The U.S. federal government has well over half a million vehicles, making up the largest fleet in the nation. The goal of the Energy Policy Act of 1992 was to replace 30 percent of U.S. transportation-related petroleum consumption with alternative-fuel vehicles by 2010, and the Act requires that at least 75 percent of vehicles purchased annually by federal agencies in major metropolitan areas be alternative-fuel vehicles. Unfortunately, federal agencies have a history of ignoring this requirement.

In November 2005, the Center and Bluewater Network won a settlement of a lawsuit against four federal agencies for their failure to make the required purchases of alternative-fuel vehicles, in which the Department of Commerce, Department of Labor, Department of Transportation and Veterans Administration admitted their violation of the Energy Policy Act and agreed to comply with the law. In 2006, a federal judge rejected a Department of Energy finding that federal agencies couldn’t take action to reduce fuel use because petroleum reduction goals mandated by the Act were unachievable.


Off-road vehicles have small, inefficient two- and four-stroke engines that emit large amounts of pollution, including carbon dioxide. In California alone, off-road vehicles spew out more than 230,000 metric tons of carbon dioxide each year, equal to the emissions created by burning about 500,000 barrels of oil.

The Center has been active in getting the state of California to address these emissions along with those of other sources under the Global Warming Solutions Act, and we’ve published a report detailing the problem and its solutions.

Photo courtesy of Wikimedia Commons/Steevven