Dense, stale, choking exhaust bellows out of the truck’s tailpipe, filtering through the air conditioning to your lungs, while thick, black layers of smog blanket the city skyline.

Aren’t we tired of all the pollution from our cars?

The fuel-cell hydrogen car may be the answer to this problem. The zero emission vehicle (ZEV) is fueled with hydrogen; a colorless, odorless, tasteless and non-toxic gas that’s one of the most renewable and abundant resources, found in 98 percent of living things on earth.

San Francisco, second to join the hydrogen bandwagon, added two compact and eerily quiet Honda FCXs to their fleet of Environmental Protection Agency (EPA) approved vehicles, leased from Honda of San Francisco for $500 a month through grants.

“We believe hydrogen is the answer to all the clean air questions,” says Gloria Chan, public information officer for San Francisco Department of the Environment. “Using San Francisco’s terrain, we hope to improve the technology so that consumers can purchase the best product possible.”

With our unique hilly terrain and broadly ranging weather climate, San Francisco is an ideal place to further test the short, metallic baby shoe-like FCX.

"They're accumulating real-world miles," says Stephen Ellis, the company's manager of alternative fuel sales and marketing. "[The city] is using them like the average user would."

A fuel cell, which acts like a car’s engine, is comprised of panels that look like stacked slices of bread. Hydrogen atoms mix with oxygen atoms from the air, and pass through the panels to produce electricity, which powers the car. The only emission out of this tailpipe is puffs of translucent water vapor, and it evaporates into the air instantly.

Currently, the city’s hydrogen cars are maintained at a central shop on Gerald Avenue in San Francisco. The central shop is just one of 15 fueling stations currently pumping emission-free hydrogen fuel into 95 vehicles—mostly city government cars—tooling around California. But with Gov. Arnold Schwarzenegger’s “hydrogen highway” plan to build an additional 16 fueling stations along the California coast, fueling your hydrogen car will soon be as simple as filling your gas-guzzler is today.

“Refueling a hydrogen car is just like pumping gas, except for an added safety latch that ensures no hydrogen spills or leaks during the refueling process,” says Faiz Kahn of the San Francisco Clean Air Program.

At a whopping $1 million per hydrogen car, it’s no wonder people aren’t quick to snatch these up. But you won’t have to shell out the money to buy a brand new hydrogen car. Current American cars will be able to be converted to the fuel cell system down the road.

By 2010, the “hydrogen highway” pumps will be complete and manufacturers like Honda, Mercedes Benz and General Motors hope to have the technology streamlined to bring down the price of the cars. Since hydrogen fuel is still a young technology, scientists are already working on special methods to eliminate the pollution created when converting fossil fuels into hydrogen fuel, before the oil light starts blinking on America’s oil reserves. Electricity produced by solar or wind power to extract hydrogen from water is one example.

“The fuel cell vehicle is a realistic pathway to sustainable transportation, and to remove our dependence on oil, imported or otherwise,” says Stephen Ellis, Alternative Fuel Cell Vehicle manager for American Honda.

So keep an eye out for the hydrogen car, because you definitely won’t smell it coming.