Breaking into the mainstream, Cornell says, would require "massive investment in infrastructure."
Even so, natural gas is not an unlimited resource, a crucial factor that hurts its viability in the long-term. "If we switch toward using natural gas," says Cornell, "we will eventually be in the same situation as we are with oil."
Hydrogen Fuel Cells
A compelling argument for erecting natural gas stations is that they can help power hydrogen fuel cells, which produces clean energy by bonding hydrogen and oxygen.
Natural gas is not only the most effective way to make hydrogen, it's cost effective and environmentally friendly, says Britta Gross, General Motor's manager of hydrogen infrastructure and strategic commercialization.
GM has plans to set up 10 fueling stations in Los Angeles and New York so that volunteers can test out the company's hydrogen-powered prototype, the Equinox, through a program called Project Driveway.
"We feel good about the technology," says Gross. "If you want something that can recharge quickly and go long distances, here is an answer for it."
Hydrogen research generated much excitement in 2003 when President Bush proposed a billion-dollar initiative to further the development of what he called "one of the most encouraging, innovative technologies of our era."
Arnold Schwarzenegger followed suit the very next year and launched the California Hydrogen Highways Network project, which aims to open a hydrogen highway in the state by 2010. The governor marked the occasion by posing for snapshots as he filled up a hydrogen-powered Toyota at a local gas station near Sacramento.
However, those who don't share the same enthusiasm say that there are challenges that need to be addressed before hydrogen-powered vehicles can be considered practical. Besides lacking the infrastructure to support it, hydrogen currently costs more than gasoline.
Romm, an outspoken critic, doubts that fuel cells will be a viable option during the first half of the century, if ever.
Until the technology lives up to the promise of not just clean, but affordable fuel, he poses the question: "Why would anybody spend billions of dollars building fueling stations that might be a wasted investment?"
Hybrid Electric Plug-Ins
With the success of hybrid cars like the Toyota Prius, some experts see next-generation hybrid plug-ins as a logical successor and an important step towards ushering in a fully electric car.
Unlike hybrids currently on the market, plug-ins are rechargeable from a wall socket and can run on pure electricity for several miles before falling back on the gas engine. RechargeIt, a project launched by Google to demonstrate the potential of plug-in hybrids, converted four Priuses and two Ford Escapes into plug-ins and found that in real-world driving tests, some cars were able to achieve 100 mpg.
Although electrical power is available for about a quarter the price of gasoline, Ron Cogan, editor of Greencar.com, says that the savings will likely be offset by the expensive cost of lithium-ion batteries.
"It's one thing to pay the extra cost of a hybrid, but adding $10,000 more for batteries only makes it affordable for highly motivated people," he says.