Environmental Defense doesn't reveal the algorithm used to generate the ratings, but Yahoo! explains that the goal is to reflect a vehicle's "total environmental impact" by juding them according to fuel economy, emissions standards and curb weight.
The pollutants covered in the rating include greenhouse gases, particulate matter, nitrogen oxides, hydrocarbons and carbon monoxide. So which is worse? Spewing carbon dioxide or particulate matter? Unfortunately, Yahoo! doesn't get detailed in their explanation of the Green Ratings. What's interesting is that they claim the ratings retain the same scale throughout the spectrum. That is, they say that the savings of the 3 points between 40 and 43 cuts down on the same amount of pollution as the 3-point gain between 60 and 63.
They've also taken up all the slack given to flex-fuel vehicles as each car's Green Rating is based solely on its use of "the commonly available motor fuel (gasoline or diesel)" unless it was specifically designed to use a different fuel such as natural gas. The site doesn't totally shun ethanol as there's a link for it under the "Technology" tab, however, none of the cars were rated with it. The same holds true for vehicles capable of running biodiesel. Their ratings are based on petroleum diesel fuel.
Check out the top 100 cars by their Green Rating by clicking here. Number 1 isn't the Prius. It's the 2006 Honda Civic Hybrid. If you're curious why the 2006 Civic Hybrid beat out the 2007 Civic Hybrid, the answer may be as simple as the vehicles' respective weights. The 2007 version tipped the scales by six more pounds than its predecessor. The highest ranking SUV is the 2007 Ford Escape Hybrid (front-wheel drive) which came in at 9 on the list. The Toyota Camry Hybrid was just above the Escape at number 8 while the Honda Accord Hybrid managed just 31st. Oh, and sports car fans will be happy to see the Lotus Elise listed at number 55 and the highest ranked Miata at 57.
When you get a chance, check out Yahoo's green autos page at http://autos.yahoo.com/green_center/ and tell us what you think.
[Source: Environmental Defense]