If automotive fuel trends paralleled the fashion industry, diesel would have a reputation for being something akin to polyester: old fashioned, uncomfortable, and kind of smelly. The reality is that, despite the less than appealing odor, diesel fills our air with fewer toxic chemicals than gasoline, and diesel engines go farther on a single tank of gas, at times rivaling - and even exceeding - hybrid fuel economy numbers.

Despite this, we still tend to think of diesel in terms of what we might get stuck behind in traffic: large trucks, and metro transit buses with rooftop exhaust pipes. Avoidance of diesel, however, is something we ought to rethink, especially for those of us who live in places where hard freezes are rare (diesel can thicken when the temperatures are too cold). Two major car makers, Audi and Toyota, are helping us to do this, by planning diesel-fueled automobiles for the U.S. market, to roll off assembly lines sometime in the next three years.

Audi was the first to tout their new diesel offerings. They've formed a division in charge of their explorations into clean diesel, which they refer to as TDI, and have it set up to find technology that will meet vehicle emissions regulations in all 50 U.S. states.

The acronym "TDI" actually stands for "turbocharged direct injection" and it refers to a collection of systems and technologies that target particulate and NoX output, and also makes sure that Audi's diesel-fueled vehicles meet California's emissions strictures, which are the toughest in the country. "TDI" also refers to the actual power-trains and diesel engines that Audi builds.

The first diesel Audi offered in the United States will be the Q7 TDI V-6 SUV, and it's designed to meet emissions standards from 2009 onward.

Audi will be including the TDI designation on their nameplates to help car buyers tell which vehicles have clean diesel technology, and all the benefits thereof, including faster acceleration and lower fuel consumption over all.

Meanwhile, Toyota has been involved in a series of negotiations with Japanese diesel expert Isuzu, over the possibility of shared technology, and will also be offering diesel-powered cars by 2012 if not sooner.

Initial reports of the Toyota-Isuzu collaboration surfaced in July, with announcements made in August that plans were going forward. Among the reports made was the news that Isuzu has invested in a plant in Hokkaido, Japan, so that they can supply 200,000 low-emission diesel engines a year to Toyota.

This collaboration cannot really be a surprising, since Toyota bought a 5.9 percent stake in Isuzu in November of 2006. Since then, the two companies have talked about sharing resources for field research, development of small diesel engines, and other alternative fuel technology.

Toyota has long demonstrated their commitment to green fuels. While they were not the first major manufacturer to offer hybrid technology in the United States (that distinction goes to rival Honda), their Prius remains the standard for the concept.

With major makers moving diesel into the U.S. market, it would not be surprising if, in a few years, instead of complaining when they are stuck behind a bus, drivers comment that they are trapped behind a car still using that old-style gasoline.

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