Hydrogen and fuel-cell cars are being mightily promoted. The U.S. Department of Energy has made them the central focus of its clean energy efforts. The state of California has said it will in the next few years build a "hydrogen highway," with hydrogen fueling stations every 20 miles along major highways. General Motors is spending more than a quarter of its research budget on fuel cell vehicles and Larry Burns, GM's vice president for R&D and planning, said in February that the company will have a commercially viable fuel cell vehicle by 2010.

Yet for all this hype, hydrogen cars are likely to remain inferior to the best gasoline-electric hybrid vehicles such as the Toyota Prius in virtually every respect-cost, range, annual fueling bill, convenience, safety-through at least 2030. The Prius will even have lower overall emissions of many pollutants than cars running on the hydrogen that is likely to be available at fueling stations for the foreseeable future. And a premature push toward hydrogen cars would undermine efforts to reduce the heat-trapping carbon dioxide emissions that cause global climate change.

For hydrogen cars to become both practical from a consumer's perspective and desirable from an environmental perspective will require at least three major technology breakthroughs. In addition, the nation will have to shift its energy policy dramatically toward renewable energy sources such as wind and solar.

Don't get me wrong. I am a strong proponent of hydrogen as a possible fuel for the future. In fact, I helped oversee the Department of Energy's program for clean energy, including hydrogen, for much of the 1990s-during which time we increased funding for hydrogen technologies tenfold. I believe that continued research into hydrogen remains important because of its potential to provide a pollution-free substitute for oil post-2030.

But going beyond R&D at this point to actually building the hydrogen infrastructure-as many advocate-is both unjustified and unwise. As Peter Flynn, an engineering professor at the University of Alberta, concluded in a 2002 study of the effort to commercialize natural gas vehicles: "Exaggerated claims have damaged the credibility of alternate transportation fuels, and have retarded acceptance, especially by large commercial purchasers."

Let's briefly look at why hydrogen cars are still a long way from making sense.