Hydrogen, unlike hydrocarbons, is not a source of energy, in that it takes more energy to get the Hydrogen than you get by using the Hydrogen in a fuel cell-it is a form of energy storage. By converting fossil fuels to hydrogen (or burning them to generate electricity to create hydrogen) you’re shifting the source of the pollutants from tailpipes to smokestacks, which may be useful in some areas where smog is a major concern. Energetically speaking, there is no practical advantage to using hydrogen except where there is some good source of “free energy” (i.e., solar, tidal, wind) and these sites tend not to be located near major poulation centers.
As mentioned above, hydrogen powered vehicles would require extensive infrastructure to be built up, so you have the “chicken and the egg” problem. Even if you had a best case scenario, such as large city in the American Southwest with abundant wind/solar production capability, you still need to build and maintain pipelines for liquid hydrogen and hydrogen refueling stations. You don’t have to go far outside the main city before this infrastructure becomes prohibitively expensive compared to our cheap, subsidized fossil fuels. The only people who are going to drive thirty miles out of their way once a week to fill up on hydrogen are the folks who are already buying the hybrids now.
Also hydrogen takes up a lot of space, and does not have the energy density of fossil fuels such as diesel and gasoline, so while it may make sense for small city commuter cars, it makes much less sense for large trucks.
Hydrogen fuel cells are never going to make sense in many parts of the country, at least not until supply becomes so low that market forces drive the price of fossil fuels so high that it starts making economic sense to use other fuels- note I didn’t say alternative sources of energy. By that time, barring any major breakthroughs in physics, biology, or chemistry, we’ll probably be using nuclear fission for electricity and converting biomass to hydrocarbons through a process like thermal depolymerization. And IMHO, we’ll have much bigger problems on a global economic scale to worry about than energy losses of heat from IC engines.
Using ethanol as a fuel, especially as practiced today, is plagued with most of the same problems as hydrogen. It costs more, energetically, to produce the alcohol than you get out of the alcohol.
Most of the energy inefficiency in our current transportation system is due to social factors, not lack of technology. We choose to drive rather than use public transportation, carpool, or bike or walk. We choose to buy vehicles with high fuel consumption. We like the look of big tires and aerodynamically dirty designs. Consumers are not asking manufacturers to incorporate fuel saving features such as lightweight materials, low rolling resistance tires and aerodynamic bodies in mainstream automobiles. These features contribute a lot to the efficiency of cars like the Toyota Prius and Honda Insight.
Furthermore, much of the fuel efficiency advantage a hybrid car has over a traditional IC vehicle has to do with power management, giving more control over energy expenditures to a sophisticated computer rather than the “nut behind the wheel”. By paying attention to maintenance and driving technique, the average driver could save quite a bit of gas, but we like to get where we are going, dammit. If you check the reviews of hybrids in motor magazines, you’ll notice that those leadfoots tend to get considerably worse fuel economy than the manufacturers claim on the EPA cycle, while owners of these vehicles often treat it almost like a game trying to maximize efficiency.
I’m generally against government intrusion, so I don’t see much difference between the government forcing change via clean air/fuel efficiency legislation or encouraging people to change their habits through direct market-based manipulation, even if the difference is really only semantics.
