America's Dirtiest Vehicles

These cars fall behind in fuel efficiency, carbon footprint and air pollution.

In Pictures: America's Dirtiest Vehicles

Starting in 2011 the Ford Focus electric sedan will be sold in 19 cities across the United States. It's built in Michigan, uses the same platform as the conventional, gas-powered Focus sedan, and can go 100 miles on a single charge of its zero-emission lithium-ion battery.
Compare that to the Buick Lucerne. The $29,730 sedan gets 15 miles per gallon in the city, and 23 mpg on the highway. All that burnt fuel dumps an EPA-estimated 10.4 tons of carbon dioxide into the environment yearly--significantly more than other cars in its class, like the Toyota ( TM - news - people ) Avalon (8.1 tons per year) and Chevrolet Impala (6.3 tons).

In fact, the Lucerne is so far behind the pack in terms of its environmental footprint that it landed on our 2010 list of the year's dirtiest vehicles, along with the GMC Yukon, Cadillac CTS and Toyota Sienna.

In Pictures: America's Dirtiest Vehicles

To be fair, all of these cars meet or exceed federal emissions standards, and are significantly cleaner than the heavy, loud, inefficient gas guzzlers our grandparents drove. Automakers are quick to defend their cleanliness: The Sienna, for instance, rates lower in terms of fuel economy because of a gas-hungry all- wheel-drive model, which competitors don't offer, according to a Toyota Motors spokesman.

Still, the cars on this list lag behind the rest of the market, and are certainly "dirtier" than other new models.
Behind the Numbers
To determine the dirtiest cars on America's roads, we looked at data from the U.S. Environmental Protection Agency for all 2011-model-year vehicles. Each car was scored for its performance in terms of air pollution, fuel efficiency and carbon footprint ratings.

Our air pollution score reflects the amount of tailpipe emissions a vehicle releases; vehicles with better scores emit fewer pollutants like hydrocarbon, carbon monoxide and formaldehyde. The carbon footprint score measures the impact a vehicle has on the environment, based on how many tons of CO2 it dumps annually. Those estimates are based on full fuel-cycles, combine all steps in the use of a fuel from production to consumption, and include carbon dioxide, nitrous oxide and methane, the three major greenhouse gases emitted by motor vehicles.
For each car, we supposed 15,000 miles driven annually, 45% on the highway and 55% in the city. The worst offenders in each of 10 automotive segments made our list.
We did not evaluate vehicles classified as "heavy duty," like the 3500 series of the Dodge Ram, which are exempt from federal fuel economy requirements. We also deliberately omitted some vehicles that rated higher on the particulate-emissions scale, including exotics like the Ferrari 599 GTO and high-performance variants like Mercedes-Benz's AMG. Many of those cars do have poor emissions and fuel efficiency ratings but are produced in such small quantities and are driven so infrequently that they don't significantly contribute to air-pollution problems.