What are some of the other alternative fuel vehicles?

Although research is continually progressing, there are no other alternative fuel vehicles available yet for mass consumption. A lot of research is being conducted into fuel cells, an electrochemical powerplant 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 it does this without combustion. Its sole emissions are heat and water vapor, with no greenhouse gases produced. An array of fuel cell vehicles from the major automakers are now in field trials in the U.S. and Japan. Most of this activity is centered in Sacramento, California, through the California Fuel Cell Partnership, although fuel cell consortia in other states, as well as in Japan, are now promoting highway demonstrations of fuel cell vehicles. Fuel cells, however, still face significant developmental issues that include durability and, especially, cost. Operation in extremely cold temperatures is also a hurdle, although Honda has recently made breakthroughs in this area with its latest fuel cell.
In recent years, some automakers have been examining hydrogen as a fuel for their internal combustion engine vehicles, beside being used in fuel cells. BMW, Ford, and Mazda are at the forefront of this effort with concept and demonstration vehicles running on either gaseous or liquefied hydrogen. Hydrogen vehicles have a long developmental road ahead of them. Perhaps the greatest challenge for them is the infrastructure. Simply, there are only a handful of places in the country where hydrogen vehicles can be fueled. A hydrogen refueling station is extremely expensive at a half-million dollars or more, making the creation of a widespread refueling infrastructure a daunting and expensive task. Still, it may come, and innovations like the home hydrogen refueling system being developed by Honda R&D and its developmental partner Plug Power could shorten the timeline considerably if they come to pass. Other alternative fuels in development are batteries powered by solar, and engines powered by ethanol, natural gas and propane.