Hydrogen cars get no respect. A lot of people consider them the stuff of science fiction, a technology as vaporous as the stuff that drives them. But despite some hurdles even Liu Xiang couldn't clear – creating a fueling infrastructure comes to mind – Uncle Sam and the big automakers love hydrogen cars and are driving across the country in a fleet of them to prove they work.

Even if they're occasionally hauled on trucks.

Hydrogen evangelists set out from Portland, Maine, today to take the gospel to 31 cities in 18 states during the two-week "Hydrogen Road Tour." Although H2 is the most common element in the universe, it can be really tough to find when the fuel gauge is approaching "E." With only 62 hydrogen stations nationwide – one opened in Massachusetts just this morning – portable fueling stations will keep the cars going when they aren't being ferried on trucks.

While some may consider that cheating, road trip organizers say it's part of the point. "Part of what we're doing with the tour is raising awareness of the need for the fueling infrastructure," Patrick Serfass of the National Hydrogen Association tells us.

The association joined the Department of Energy and the California Fuel Cell Partnership in organizing the tour, which hopes to convince people hydrogen is a viable fuel on the cusp of commercialization. "The technology needed to put these cars on the road, and keep them moving, exists today," says Paul Brubaker, head of the federal transportation department's Research and Innovative Technology Administration. "The question is not if hydrogen powered vehicles will be available commercially, but when."

For all its promise of emissions-free motoring, hydrogen has more than its share of naysayers, but that isn't keeping the auto industry from pouring hundreds of millions of dollars into developing cars that run on it. Honda's leasing the FCX Clarity (pictured) fuel cell vehicle and made a big deal about actress Jamie Lee Curtis picking one up last week. Other celebrities - including Jay Leno, Edward Norton and Will Ferrell - are driving the BMW Hydrogen 7, which also runs on gasoline. General Motors plans to put 100 Equinox fuel cell vehicles in driveways and Toyota's developed a fuel cell vehicle with the unprecedented range of 516 miles. Even Mazda's getting in on the act with a hydrogen-fueled RX-8 that could be in showrooms by 2012.

BMW, Daimler, Ford, GM, Honda, Hyundai-Kia, Nissan, Toyota and Volkswagen have cars making the road trip, and they'll be joined along the way by fuel cell buses run by some of the nation's six transit agencies that use them. "These hydrogen vehicles are the non-polluting cars of tomorrow and they are being demonstrated today on our nation's roads," says Thomas Barrett, deputy secretary of energy.

There are many challengesto overcome before hydrogen vehicles are viable, not the least of which are making the cars affordable and producing and distributing hydrogen on a large scale. Still, the California Fuel Cell Partnership says thousands of hydrogen vehicles and hundreds of buses could be on the road by the end of 2016 and they'll fill up at hundreds of stations. In "Vision For the Rollout of Fuel Cell Vehicles and Hydrogen Fuel Stations," the partnership predicts fuel cell vehicles in California will need 5,250 kilograms of hydrogen each day by the end of 2014.

California has 26 hydrogen stations and 10 more planned. The partnership offers "a rough estimate" that capital costs for early stations will run $2 to $4 million – excluding land and operating costs - and "the State of California should plan to spend $80-$90 million over four years (2010 through 2014) for hydrogen fuel stations to support the pre-commercial vehicle phase."

Until then, you may want to stay close to one of the nation's 62 hydrogen stations. Or have a flat-bed truck follow you.

Photo by Honda