Hybrids? Some opt to go all-electric.

It is also unlikely Toyota would make a plug-in Prius - though "nothing is impossible," he hedges. The problems are many, including a "much, much, much larger battery" needed to increase range, which would add hundreds of pounds, says David Hermance, a Toyota environmental engineer.

Anyway, plug-in hybrids are not that green, Mr. Hermance argues. They run on electricity that's often created by coal-fired power plants. So, such a car would be only marginally better from an environmental and economic perspective than a regular hybrid and have limited appeal, he concludes. Case closed.

While Andrew Frank concedes that an electric car powered indirectly by coal isn't much better for the environment, he argues it is still more efficient transportation - and it makes a world of difference from the standpoint of energy security.

With engineering students at the University of California at Davis, Professor Frank has spent more than a decade turning production vehicles into plug-in hybrids using off-the-shelf parts. "We just built a high-performance plug-in hybrid Ford Explorer," he says. "It's 325 horsepower - 200 of that horsepower is electric and 125 is gasoline. This car goes like a rocket, but still gets double the fuel economy of a regular hybrid. And for the first 50 miles it is all electric - zero emissions."

That's enough for many drivers to complete their daily commute. Compared with conventional cars, the annual fuel consumption of the modified cars "is only about 10 percent, because you're using gas so infrequently," he says. "Our studies show [that] the average person would only go to the gas station six times a year compared with maybe 35 times a year."

Built on a stock Explorer platform, the hybrid retains all its original interior space. There is also more space in the engine compartment because the vehicle lacks moving parts like a fan belt, generator, water pump, and even a transmission. Because it has fewer than one-fifth the number of moving parts of a conventional SUV, the hybrid's weight, even with a heavier battery, stays the same. Assembly is simpler and reliability, better. In production, it might cost $40,000 or less, he says.

Despite repeated presentations to the Big Three automakers in Detroit, Frank has received little interest from them. But last year, Toyota flew his Explorer to its research facilities in Japan so engineers could pore over the vehicle. "There's no question in my mind that Toyota has plans for a plug-in hybrid right now, but they aren't talking about it," he says.

Certainly, plug-in hybrids are for real. DaimlerChrysler is reportedly near delivery of the first batch of what is expected to be as many as 100 Sprinter delivery vans that permit travel of up to 20 miles on electricity alone. This will come in handy in car-clogged European cities currently considering bans or other limits on gas- and diesel-powered delivery vehicles.

AC Propulsion had demonstrated a converted VW Jetta with a plug-in hybrid electric vehicle (PHEV) system. Renault is offering its Kangoo PHEV that can go 60 miles on a charge before switching back to gas. Commuter Cars Corp. of Spokane, Wash., is offering a low-volume electric car called the Tango for $85,000.

Meanwhile, a not-for-profit outfit called CalCars in San Francisco is modifying two Priuses by adding more battery power and a plug. The group has discovered an empty space under the hatch near the current battery that looks almost as if Toyota intended to do this itself one day. "We hope to get significantly more miles per gallon with the additional battery power," says Felix Kramer, the group's founder. "Our purpose is to show Toyota that there is demand for this kind of vehicle."

Will Toyota - or Detroit - respond? Not without major breakthroughs in technology, says Dan Bedore, a Ford spokesman. "It's become pretty clear that our ... non-plug-in hybrid system is the direction we see the market going."

"The answer is they really don't want to do it," Frank says. "We're just a bunch of students. If we can build this with off-the-shelf technology, they can too - and do things better than what we do. If they really were interested in doing something in the short term, they could do it."

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