Best and Worst Automakers

Our analysis reveals significant differences between automakers based on their commitment to producing the cleanest new vehicles.

Find the best and worst automakers.

Learn what automakers can do to improve air quality and health.

Trends within the Top 10 Automakers

The average Auto Asthma Index scores for the 10 major automakers range from 6.0 to 8.1 over the past 6 model years. GM and Daimler-Chrysler fare worst, with the highest average scores for their recent vehicles. Mazda and Honda are producing the cleanest newer autos, with average scores of less than 7 for recent vehicles.

Average score for the Big 10 Automakers on the Auto Asthma Index, 2001-2006 vehicles.

One explanation for this variation is the automaker's commitment to using the cleanest technologies. Honda, Nissan and Ford have taken initiative to voluntarily adopt more stringent pollution controls for their vehicles ahead of federal mandates. [Friedman 2004] However, GM, Daimler-Chrysler and Ford continue to have worse scores than other automakers because they make more-polluting large vehicles relative to Mazda and Honda, who focus their efforts on cleaner burning cars, as well as smaller trucks, SUVs, vans, and minivans. Daimler-Chrysler's negligent attitude toward pollution and public health is demonstrated by their recent $90 million settlement with EPA for installing defective emissions controls in nearly 1.5 million Jeep and Dodge vehicles between 1996 and 2001, and then covering up the problem. [EPA 2005]

How well do common brands stack up?

By taking a closer look at automaker subsidiaries, we see that GM's Saturns averaged a respectable 7.0 on the Auto Asthma Index, while their Hummers averaged 9.6. Ford's Mercury had the best score of 5.9. But these good performers are weighed down by Ford's Land Rovers, with an average score of 8.1.

To analyze subsidiary company performance, we investigated automakers by division. We calculated average Auto Asthma Index values for vehicles manufactured between 2001 and 2006. We also determined the average Index values for those vehicles manufactured between 1996 and 2000, using real world emissions measurements obtained from California Smog Check records.

According to our analysis, the dirtiest divisions include Hummer, GMC, Isuzu and Chevrolet. These divisions produce many of the largest and dirtiest vehicles available today. The cleanest divisions include Mercury, Honda, Buick, Acura, Aston Martin, Mazda, and Jaguar, with average Index values of less than 7. These divisions primarily sell passenger cars as opposed to trucks, SUVs, vans and minivans, and make an effort to produce vehicles that meet the most stringent California and federal emissions criteria.

The average Auto Asthma Index values calculated for older vehicles from real world Smog Check emissions measurements do not show the same trends with division as the average Index values calculated for newer vehicles using EPA data. These contrasting values suggest divisions' changing priorities concerning clean vehicles, as indicated by the relative quality and durability of the emissions control technology installed on newer and older vehicles.

What can automakers do to improve air quality and health?

To meet the more health protective emissions requirements for the cleanest federal and California vehicle categories, automakers have already developed a broad range of technologies that can vastly reduce a vehicle's contribution to smog. Many of these technological solutions are surprisingly inexpensive. [UCS 2005, Healey 2003] By buying the least polluting cars and trucks available, we can use our dollars to demand that automakers install existing clean car technologies on all vehicles to prevent pollution and improve public health. Here are some ways that automakers can reduce smog:

• Make more of the cleanest cars.

BMW, Ford, Honda, Hyundai, Kia, Mazda, Mercedes-Benz, Mercury, Mitsubishi, Nissan, Subaru, Toyota, Volkswagen and Volvo are all selling model year 2006 vehicles that meet the new partial zero emissions vehicle (PZEV) standards. (What are the cleanest cars? Where would I purchase one?) These vehicles emit less than 10 percent of the smog chemical pollution of a typical 2006 passenger car, which has an Auto Asthma Index of 7. Their emissions control equipment is also guaranteed to last for 150,000 miles of driving, instead of just 100,000 miles. Emissions control technology must be designed to last given that newer cars are lasting longer and are driven more miles each year than older models. Automakers have shown that they can make clean, reliable autos using available technology--now they should take the next step and install this equipment on all of their vehicles.

• Improve emissions control equipment.

The catalytic converter removes many smog-forming chemicals from exhaust before releasing it through the tailpipe. Improved materials, leak-free exhaust systems, finely controlled temperature and air-flow, and supplemental systems to clean exhaust before the catalytic converter has warmed up, can reduce smog chemical pollution from our cars and trucks.

• Improve engines.

When gasoline is burned inefficiently, more pollution is produced. Well-designed engines with improved fuel delivery systems can encourage efficient gasoline combustion and reduce oil use, creating fewer smog chemicals.

• Catch problems with better on-board diagnostic systems.

Installed in all new vehicles, on-board diagnostic systems let us know when problems with the engine or emissions control equipment are producing excessive pollution. Improvements in these systems will allow us to repair broken cars and trucks before they create too much smog.


Environmental Protection Agency. 2005. U.S. announces $94 million Clean Air Act settlement with Chrysler over emission control defects on 1.5 million Jeep and Dodge vehicles. Press Release, December 21, 2005.

Friedman D, MacKenzie D. 2004. Automaker Rankings 2004: The Environmental Performance of Car Companies. Union of Concerned Scientists, Cambridge, MA.

Healey JR. 2003. Cleaner cars take toll on automakers' costs. USA Today. September 16, 2003.

Union of Concerned Scientists. 2005. Backgrounder: Light trucks and air pollution.
light-trucks-and-air-pollution.html Updated 2005

INDEX (1996-2000)**
Hummer 9.6 n/a
GMC 9.1 8.1
Isuzu 8.9 8.5
Chevrolet 8.5 7.7
Oldsmobile 8.3 6.7
Pontiac 8.2 7.0
Land Rover 8.1 n/a
Dodge 8.1 8.7
Ford 8.0 6.6
Bentley 8.0 n/a
Daewoo 8.0 6.4
Lamborghini 8.0 n/a
Rolls-Royce 8.0 n/a
Porsche 8.0 6.2
Audi 7.8 8.5
Lincoln-Mercury 7.8 n/a
Mercedes-Benz 7.7 4.5
Hyundai 7.6 6.0
Lexus 7.6 7.9
Toyota 7.6 8.4
BMW 7.6 6.6
Jeep 7.6 8.7
Ferrari 7.6 n/a
Mitsubishi 7.4 6.1
Saab 7.3 6.2
Volkswagen 7.3 6.2
Chrysler 7.3 8.0
Volvo 7.3 5.6
Infiniti 7.2 7.9
Subaru 7.2 n/a
Nissan 7.1 7.5
Saturn 7.0 6.6
Suzuki 7.0 6.3
Kia 7.0 6.4
Cadillac 7.0 8.1
Jaguar 6.9 5.3
Mazda 6.6 7.4
Aston Martin 6.3 n/a
Acura 6.2 7.9
Buick 6.1 6.1
Honda 6.0 6.7
Mercury 5.9 5.6
*EPA data
**Smog Check data

Read the report and learn about how cars contribute to America's asthma epidemic. Smog causes lifelong damage to our children's lungs.

The Cleanest Cars

2002 Lincoln-Mercury Continental
Check the Auto Asthma Index for a different vehicle.