What's Next?

Although hybrid electric vehicles go a long way toward reducing consumption of non-renewable fossil fuels and reducing air pollution, they are only the beginning.

Fuel-cell and internal combustion vehicles powered by hydrogen currently represent one of the most high-profile alternative fuel efforts by automakers. Fuel cells efficiently produce electricity from hydrogen to power electric drive motors and do so without combustion, which means no greenhouse gases are produced in the process. Amazingly, the major byproducts are heat and water.

Honda's limited-production FCX is at the forefront of efforts to develop hydrogen-powered fuel-cell vehicles.

Fuel-cell vehicles, like Honda's experimental FCX, likely have a decade of development still to go before being mass marketed. Cost to produce fuel-cell stacks and other components is still prohibitively high. Plus, refueling infrastructure and sourcing mass quantities of hydrogen remain major obstacles. Only a handful of hydrogen fueling stations exist, although more are being built.

Internal combustion engines can also be modified to run on hydrogen, with near-zero emissions. Less costly hydrogen internal-combustion-engine vehicles now being explored by BMW, Ford and others could pave the way for fuel-cell vehicles and encourage a hydrogen-fueling infrastructure to be built sooner than later. A firm called Energy Conversion Devices is currently exploring the possibility of converting the Toyota Prius to run on compressed hydrogen instead of gasoline.