A funny thing has happened on what U.S. policy makers thought was going to be the high road to a hydrogen economy. Initiatives aimed at putting hydrogen fuel cell-powered cars on the road by 2020—visualized by President George W. Bush in his 2003 State of the Union address as the centerpiece of his plans to wean the country from fossil fuels—are taking longer than promised. At the time of the speech, hybrid-electric cars, which offer higher fuel efficiency than regular cars because of electric motors that help drive the wheels, were seen in the United States as but a minor detour or way station en route to a world of hydrogen fuel cells.

But they suddenly are looking like the main way to go, or even maybe the ultimate destination. Models produced by companies such as Toyota Motor Corp., in Toyota City, Japan, and Honda Motor Co., in Tokyo, are flying out of dealer showrooms. Among those who have been able to purchase hybrids (usually after a two- to six-month wait) are some early adopters—like a group of physics professors at Harvard University, in Cambridge, Mass.—who have made tinkering with hybrids their primary extracurricular activity.

Now, a derivative of hybrids that will improve fuel economy even more by maximizing the use of the electric motor is poised to make what is already an undeniably attractive concept downright irresistible. Some of the most eager owners of the Prius, the world's most popular hybrid, have been hacking the cars, swapping their 1.3-kilowatthour battery packs for bigger ones with capacities as large as 9 kWh.

The modifications also include the addition of plugs so the new, bigger battery packs can be recharged from wall outlets. The resulting machines, referred to as plug-in hybrids, can be propelled exclusively by their electric motors for, in some cases, more than 30 kilometers without their gasoline engines ever turning on. The factory-built Prius can run on electricity only, but for just a kilometer or two.

This group of hackers and other technologists say that in a few years, we could have a car that, after its batteries are topped up overnight via a wall socket, could handle a daily commute using only electrons for fuel—unlike the hybrids on the market now, which still derive all their power from gasoline [see box, "Stretching the Hybrid's Electric Capabilities]." and illustration, "Charging"].

Dramatizing the potential of the plug-in during the Tour de Sol race from 13 to 16 May in Schenectady and Albany, N.Y., a modified Prius equipped with a fully charged 9-kWh lithium-ion battery pack achieved 2.31 liters per 100 km (102 miles per gallon) on a 240-km course. It is representative of the modified hybrids that clean-car promoters and hobbyists have been building, partly for fun, partly to show how wide adoption of plug-ins could lead to dramatically lower gasoline consumption and oil imports.

Because of that promise, a strange-bedfellow alliance of environmentalists and security hawks has emerged. They are united by a conviction that the hybrid—not the futuristic fuel cell-driven hydrogen vehicle favored by the Bush administration in its FreedomCar program and other initiatives—is the way to cut both noxious emissions and oil dependence right now.

In a manifesto issued last fall in the form of a letter to the U.S. public and then again last March as an open letter to President Bush, a group representing foreign policy intellectuals and advocates of clean energy called for the "technological transformation of the transportation sector through what might be called 'fuel choice.'" The group supports increased reliance on alternative fuels that are domestically produced, such as gasohol and biomass, and on cars such as plug-in hybrids that can draw energy from the grid.

"The United States should implement technologies that exist today and are ready for widespread use," the group said in its core statement, "Set America Free." In effect, the report pits a group that includes influential Republicans against a Republican president on the question of whether the country should continue to spend several hundred million dollars a year to promote far-off hydrogen vehicles when it could do more today to accelerate adoption of hybrid-electric and alternative-fuel vehicles.