2009 Jeep Grand Cherokee LimitedEnlarge Photo
That old capitalist tool, Forbes magazine, has issued a list of the 10 dirtiest cars sold in the U.S. At the very top, in first place for filth, is the Jeep Grand Cherokee. But it turns out there are some problems with their list.
There's history behind this. A decade ago, the website for Forbes magazine practically pioneered the concept of Top-10 lists online. Remember "10 Best Colleges for Successful Topless Teenage Wealthy Cheerleader Executive Entrepreneurs"?
Unfortunately, the cars Forbes flagged has some serious methodology errors (and one wrong photo), as more than 40 commenters--including BMW fans, Jeep owners, electric-car boosters, and one who doesn't believe that climate change is real--swiftly pointed out.
2009 BMW M5Enlarge Photo
And the winners are...
So which cars does Forbes say are the 10 dirtiest? Starting with the worst (parentheses include air pollution and greenhouse-gas scores; and EPA city/highway mileage ratings), they are:
2006 BMW M6Enlarge Photo
Tailpipe emissions + greenhouse gases
We gotta say, the dirty-car list seemed like a promising piece of work. Forbes created a simple metric: multiplying the tailpipe-pollution and greenhouse-gas emission ratings from the U.S. Environmental Protection Agency (EPA) for passenger vehicles.
Each is rated by the EPA on a scale of 0 (worst) to 10 (best). Greenhouse-gas emissions tracks pretty closely to fuel efficiency, but in the case of a tie, the vehicle with the higher EPA gas-mileage rating won.
Tailpipe emissions include hydrocarbons, carbon monoxide, nitrous oxides, formaldehyde, and particulate matter, all hazardous to human health. They were first regulated in California, with national standards following in the early Seventies. Greenhouse gases include carbon dioxide, nitrous oxide and methane, all of which have been judged to alter long-term climate balance.
2008 Chevrolet TrailBlazer SSEnlarge Photo
Methodology for any of these lists can be tough. But we noticed several things right off the bat: Three of the 10 are already out of production (the Trailblazer, Aspen, and Durango). That takes care of them.
Commenters had already noticed that Forbes had removed a sentence from an earlier version that claimed, "We did not evaluate models that will end production after this year." Clearly that's not true.
More interesting, many Dodge and Jeep owners wrote to say their real-world mileage was far, far higher than these numbers. Some charged anti-Chrysler and anti-American bias. But those gas-mileage ratings do look low, don't they?
Turns out that all five Chrysler vehicles list the emissions and fuel-economy ratings for the flex-fuel engine option running on E85 ethanol. Because ethanol has less energy per gallon than gasoline, its fuel economy is correspondingly lower. But that number has no relation to the gasoline mileage that actual drivers achieve in real world use.
After about 40 comments, author Hannah Elliott added a note saying, "For all of the vehicles profiled, we selected the worst-efficient [sic] trim level and engine listed in the EPA data."She added, "We wanted to show just how dirty the worst variants could be."