Hyundai, which tied for second in the Union’s ranking of the eight largest automakers. In ranking the “greenness” of the companies — which account for 92 percent of cars sold in the United States — the Union examined the average per-mile smog pollution and greenhouse gas emissions of each automaker’s entire fleet.

“It was a photo finish, but Honda is still the champ,” Jim Kliesch, a senior engineer in the Union’s clean vehicles program, said. “Toyota was poised to take the lead but stalled in its efforts to reduce carbon emissions. Meanwhile, Hyundai’s fleet saw dramatic efficiency improvements, pushing the company into a title contender spot.”

As usual, American automakers brought up the rear.

This is the fifth time since 1998 that the Union has ranked the biggest automakers. In compiling the “Automaker Rankings 2010,” (.pdf) the number crunchers at the Union examined the per-mile smog and greenhouse gas emissions of each companies’ 2008 lineup, the latest year for which full data were available.

Each company is ranked against the industry average of all eight companies combined. The average CO2 emissions of the eight automakers was 429 grams per mile. The average emissions of nitrogen oxides and non-methane organic gases — two major smog-forming emissions — was 0.147 grams per mile. The industry average was assigned a score of 100, and each automaker was ranked against that.

Honda finished with an overall score of 86, meaning its fleet is 14 percent less polluting than the industry average. Toyota and Hyundai followed with 87 points. Volkswagen was fourth with 90, while Nissan came in at 93.

“As with the past four awards, we accept this fifth honor as both recognition of our success and a challenge for the future,” John Mendel, executive VP of American Honda Motor Co. said in a statement. “We continue to accelerate our efforts to improve fuel economy and reduce emissions that contribute to global climate change.”

And then there were the American automakers. Ford remained the best of the worst, so to speak, with a combined score of 108. General Motors followed with 109. Perennial cellar-dwellar Chrysler scored 113.

“Chrysler does what’s required by law and not much more,” Kliesch said. “When it comes to environmental performance, Chrysler managers need to get their head in the game.”

One interesting point to emerge from the data is an automaker can offer a full line of vehicles — from compacts to SUVs, as Honda and Toyota do — and still offer an eco-friendlier lineup. That pretty much kills the argument that cranking out nothing but econoboxes is the only way to be “green.”

Everyone — including Chrysler — has shown steady improvement since the Union compiled its first report in 1998, something Kliesch attributes to tightening fuel economy and emissions regulations and constant hounding by state and federal regulators.

“One of the analysis’ clear findings is that clean car policies work,” he said. “There’s great ingenuity i nthe auto industry, and better products are already beginning to reach the market. In coming years, stronger standards will guarantee that consumers reap these benefits.”

Indeed. Given all the changes in the auto industry during the past two years, things could be very interesting next time the Union ranks automakers. Hummer was still a part of General Motors in 2008, for example, and most of the automakers were still pushing SUVs in a big way. But tightening fuel economy regulations and changing consumer demands have automakers embracing smaller cars — the Chevrolet Cruze and Ford Fiesta are two examples. We’re also seeing more hybrids, and the first cars with cords — the Chevrolet Volt and Nissan Leaf — roll into showrooms at the end of this year. It should be interesting to see if and how electric vehicles effect the rankings.

With so many changes afoot and everyone striving for greater efficiency, Honda may lose its grip on the title. Whether Chrysler climbs out of the basement is another story.

UPDATED 12 p.m. Eastern to include comment from Honda.

Photo: Honda. Rich Ysfeldyke installs an instrument panel in a Honda Accord at the company’s factory in Marysville, Ohio, on the same day the factory built its 10 millionth car.

The results of the Union’s “Automaker Rankings 2010? analysis of automakers’ fleet emissions. Honda includes Acura, Toyota includes Lexus and Nissan includes Infiniti, just as General Motors includes all GM lines.

Authors: Chuck Squatriglia

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