For the fifth consecutive time, Honda earned the title of Greenest Automaker for its efforts of maintain low smog and greenhouse gas emissions levels in its fleet.

But Toyota and Hyundai aren't far behind in the latest analysis from the Union of Concerned Scientists, which ranks eight large automakers on the environmental performance of their vehicles. Its average score suggests Honda's fleet is 14 percent cleaner than the average score of the collective group. The Big Three auto manufacturers -- General Motors, Ford and Chrysler -- again rounded out the bottom of the list.

"It was a photo finish, but Honda is still the champ," Jim Kliesch, a senior engineer in UCS's Clean Vehicles Program and the author of the analysis. "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."

The UCS has evaluated automakers on the average global warming and smog emissions levels five times since its first analyzed model year 1998 vehicles. The eight carmakers -- Honda, Toyota, Hyundai, Volkswagen, Nissan, Ford, General Motors and Chrysler -- produce the best-selling vehicles in the U.S.

The fleet average environmental scores by manufacturer are below. The lower the score, the better the fleets' performance.

Honda          86       
Toyota          87
Hyundai        87
Volkswagen  90
Nissan          93
Ford              108
GM               109
Chrysler        113

The analysis found that two of the three top-ranking automakers produce vehicles in seven of eight vehicle classes. "Clearly, claim to the crown does not occur through the production of small cars alone," the analysis said.

In fact, the top-ranked carmakers receive better scores because they deliver "best- or near-best performance, both on smog-forming and global warming emissions, in nearly every vehicle class." The report points to Honda and Toyota as examples since both placed at the top of the heap in four of the seven class categories. Last-place Chrysler didn't finish first or second in any vehicle class.

Overall, however, the evaluation noted that all automakers did improve in terms of per-mile smog-forming emissions, largely due to state and federal regulations. This regulatory driver promises to play a role in the future environmental performance of carmakers as new fuel economy and emissions standards take effect over the coming years.

Image CC licensed by Flickr user Steve.M~.