I'm an education historian, not a physicist or an engineer, but there's one thing that connects my professional concerns with my citizen's interest in energy conservation: the health of poor children. After reading Richard Muller new book, Physics for Future Presidents (which explains that a chocolate-chip cookie has more energy than TNT, gram-for-gram), I'm convinced that not only is my concern with childhood asthma and diesel trucks warranted, but it will be easier to make commercially-viable zero-emission garbage trucks than zero-emission sedans. And it's all in the physics...
In 2002, NYU researcher George Thurston gave a bunch of kids pollution detection equipment in backpacks and had them troop around their Bronx neighborhoods and schools for three years, to find out where particulate and other pollution was the worst, and from what sources. The results of that study were published in 2006, became the subject of a New York Times story, and confirmed what community activists and Jonathan Kozol had said for years: for poor children who live or attend school in the South Bronx near highways, or on the routes that garbage trucks take to nearby dumps (and therefore clog as they line up waiting to get in), they are exposed to disporportionately great amounts of pollution of the sort that is well connected by research to asthma.
That's the problem. With current technology, the short-term solution is switching short-range trucks to natural gas as a fuel, something that would make garbage and recycling trucks far less of a point pollution source.
The long-term solution may take all the sexiness out of hydrogen fuel cells, but it's based on reasonable physics. As has been discussed by people far more versed in the science than I am, hydrogen is an energy transportation option, not an energy source. And while hydrogen has far more energy carrying capacity than gasoline for any unit of mass, it is far less dense, even in a liquid form. So it's not a feasible option for sedans, with their limited space. What types of vehicles have loads of space, where a less dense but more powerful fuel would be a pretty good option? Muller points out that airplanes may or may not be such a vehicle, but trucks certainly would be.
That's right: your local garbage truck is a better target for fuel-cell technology than your car or the airplane you fly. I'm going to skip the physics and economics of batteries, because even if they're marginally viable for cars (Muller argues only for hybrid-electrics), they wouldn't be for trucks. But I will argue that even if we throw away all the other considerations, there is a plausible (and I think convincing) argument for fuel-cell research on the grounds of environmental justice. I don't care if you or I ever get to drive a sports car that's all-electric or uses fuel cells. I do care that we eliminate garbage trucks as roving point sources of pollution, and if hydrogen fuel-cell technology will do that, damnit, we need hydrogen fuel-cell garbage trucks.
Needless to say, I highly recommend Muller's book, and you can find on iTunes his Berkeley Physics 10 lectures (whose title, Physics for Future Presidents, became the book's).