Even as auto manufacturers develop their array of hybrid, alternative fuel and highly efficient gasoline vehicles, there's a growing belief that the most viable longer-term alternative fuel for mass production may be hydrogen, with its most logical application being the hydrogen fuel cell.

A fuel cell is an electrochemical power plant fueled by hydrogen that creates electricity for driving a vehicle's electric drive motors. Its great advantage is that it's more than twice as efficient as an internal combustion engine in transforming energy into power - and that it does this without combustion. Its sole emissions are heat and water vapor, with no greenhouse gases produced.

In recent years some automakers have been examining hydrogen as a fuel for their internal combustion engine vehicles, as well as for fuel cells. Hydrogen vehicles have quite a developmental road ahead of them, so don't expect to see them on the highways in large numbers for some years. Fuel cells still face significant developmental issues that include durability and cost. Operation in extremely cold temperatures is also a hurdle.

Perhaps the greatest challenge for hydrogen vehicles is that of infrastructure. Simply put, there are only a handful of places in the country where hydrogen vehicles can be fueled. A hydrogen refueling station is extremely expensive, making the creation of a widespread refueling infrastructure a daunting task.