Driving a Prius can be a tantalizing experience: You've got the engine warmed up, you're going 30 mph on flat ground, the motor is a nearly silent electric purr, and you watch the bars on the gas-mileage screen mount happily up to 99.9 — infinity! Then you hit a hill, have to step on the gas, and those bars plunge into the teens. You might as well be driving a Hummer.

Getting into Dave Moore's car is like stepping into a Prius owner's fantasy. You just stay in that silent sweet spot, mile after electric mile. Though his car looks like an ordinary Prius — not even any bumper stickers announce it's anything different — Moore, a Microsoft alum, has converted it into a plug-in. He averages well over 100 miles per gallon of gas — on some tanks he's gotten as high as 175 miles a gallon — thanks to the extra batteries under the hood and the wall socket in his garage where he plugs the car in each night. Within the next few years, thousands of ordinary car owners may be able to do the same.

At an additional cost of $30,000 after purchasing the Prius, Moore's conversion is not yet an option for the masses. Still, it was easy — he bought the kit and installation off the shelf from a Colorado company — and cheap compared to the $80,000 he otherwise would have put into a high-end auto. Several other well-to-do tech geeks in the Seattle area, and more than a hundred nationwide, have done the same.

"Guys who could buy Lamborghinis are doing this instead, helping create the market for efficient transportation and demonstrating that the technology works," explains Rich Feldman, formerly state coordinator for the Apollo Alliance, an environmentalist-labor coalition pressing for development of clean-energy industry. Feldman now is a senior policy advisor to Seattle Mayor Greg Nickels.

Meanwhile, a number of Washington agencies, from the city of Seattle and King County to the Port of Chelan, have invested in plug-in conversions. The city, King County, the Port of Seattle, and other local agencies recently announced a year-long demonstration with 13 converted Priuses, at a cost of $12,000 each. The company providing the conversion kits, A123 Systems, has announced that by the second quarter of this year it will be offering these kits to the general public in five cities, including Seattle, for five figures — $9,995 each, close to mass-market affordability. The moment advocates of high-efficiency transportation have been waiting for may be arriving.

Introduction of electric cars has been stymied by a circular problem: For companies to start mass producing the cars, they have to be assured there's a sizeable market for them. For there to be a market, the price has to be reasonable. To get the price down, there has to be mass production. Individuals like Moore and agencies like the city of Seattle are playing a crucial role by beginning to create a market and testing and refining the technology in action.

"Batterymakers need volume orders to reduce costs," U.S. Rep. Jay Inslee, D-Wash., a long-time advocate of energy-saving technology, said in response to the announcement of the demonstration project. "This project and others like it will help speed the process of making plug-in hybrid vehicles available to Americans in each and every state by breaking this logjam."

Batteries have been the main technical problem for plug-in cars. As Moore explains, you need a battery powerful enough to power a car for significant distances (his will take him 30 miles at speeds under 40 mph), yet light enough not to weigh the car down. It should charge quickly and last for years. And it better not catch fire. The most promising battery technology is based on lithium ion chemistry, the same type as power laptop computers. But as a few owners of Apple, Dell, and Hewlett Packard laptops can attest, those batteries sometimes burst into flames — bad enough in a computer, disastrous in a car.

That's where A123 Systems, which made Moore's batteries, comes in. They've developed a lithium ion phosphate battery that won't catch fire. Theirs is the first conversion kit to be crash-tested and EPA certified. Kirkland's Green Car Company will do local installations of the kits. The technology is so promising that GM has signed A123 to supply the batteries for its long-awaited plug-in hybrid Volt and a plug-in version of the Saturn Vue. GM has given no date for the release of the Vue plug-in, but it promises a Volt prototype will be ready by Easter, and the car is supposed to be commercially available in 2010.

For a change, Detroit may beat Japan to the punch. Toyota doesn't appear likely to be marketing plug-in Priuses anytime soon, because, explains Moore, its battery supplier, Panasonic, is still working with the older nickel hydride batteries that power the current generation of Priuses. Mitsubishi may have a plug-in for sale in Japan as early as this year, but its diminutive MiEV will be all-electric, not a hybrid, and may be a hard sell in the U.S. market. A Norwegian firm plans to market its Think City car in the U.S. next year, but it, too, will be hampered in the U.S., by its small size, low maximum speed, and lack of a gas option. Meanwhile, Subaru announced in December that it will have its all-electric car ready for sale in Japan a year early, in 2009, and ready for wider distribution in 2012 or 2013.

In an exchange worthy of professional wrestling, Toyota's head of R&D dismissed GM's announcements about the Volt, and GM CEO Bob Lutz responded by saying Toyota would "have egg on their face" come Easter.

There's reason for skepticism, particularly toward Detroit. The movie Who Killed the Electric Car documents how GM pulled the plug on an earlier generation of electric cars, and the Think car company was salvaged by the Norwegians after Ford dumped it. As Dave Moore wearily points out, car and battery manufacturers make announcements that mass-market plug-ins are just around the corner every six months. And not so long ago, President Bush and others were hyping hydrogen as the future of the automobile.

Is the plug-in hybrid "the flavor of the month or is it genuinely coming?" asks Pat Mazza of the Seattle-based nonprofit Climate Solutions. He's modestly confident that the big automakers really will be mass marketing plug-ins by 2010 or 2012. "There's been a rapid convergence on plug-ins. Along with biofuels, this is popping up as the major thing for reducing oil consumption." Feldman and other experts say that improving and mass-producing battery-powered cars seems much more achievable than making hydrogen fuel cell cars.

The Northwest is well placed to embrace plug-in hybrids. Washington ranks sixth in the nation for hybrid ownership, and whereas in the coal-powered Midwest electric transit might not be such a hot idea, here most of our electricity comes from non-fossil-fuel-burning hydro power. Transportation is responsible for 60 percent of the state's carbon dioxide emissions. Powering cars with electricity would be a significant step toward reducing the region's production of greenhouse gas.