Mass. to retrofit hybrid vehicle fleet to plug in

40 modifications planned after 1 Prius racks up the miles

Phil Giudice, commissioner of Energy Resources, plugs in a Prius. (David L. Ryan/Globe Staff)

Pop the hood on the state's new plug-in hybrid and there is a regular Toyota Prius engine and a few dead leaves. But go for the spare tire in the trunk and you'll get a look at the battery and bumper electrical outlet that make this car special.

"So far we've been averaging 100 miles per gallon," said David W. Cash, assistant secretary for policy at the state's Executive Office of Energy and Environmental Affairs, which will be using the battery- and gas-powered car. He took the car out for a spin following its debut yesterday at the New England International Auto Show.

"You run out of charge, run on gas. You run out of gas, you fill up," said Robert Keough, a spokesman for the energy and environmental affairs office, who was riding along.

The white four-door - which was part of the state's vehicle fleet and has been driven 46,558 miles - was retrofitted with a lithium-ion battery made by A123Systems of Watertown for about $10,000. It charges from a standard electrical outlet, and a dashboard monitor tracks its efficiency as it uses either battery or gas-power.

"This is another step along the way to a greener energy future," Philip Giudice, commissioner for the state Department of Energy Resources, an arm of the energy and environmental affairs office, said at the car's unveiling inside the Boston Convention & Exhibition Center. The plug-in will replace a 20-miles-per-gallon 2003 Ford Taurus. It is expected to save about 500 gallons of gas annually and reduce carbon dioxide emissions by about 4 tons. A regular gas-electric Prius gets about 50 miles per gallon in city driving.

The state has plans to retrofit and test-drive about 20 plug-in cars for official use - funding half the conversions with money from the federal Congestion Mitigation and Air Quality Improvement Program. Giudice said the state also hopes to front half the cost, or $400,000, to purchase and retrofit another 20 cars to be tested by local companies. That money will come out of the nitrogen oxide allowance funds managed by Giudice's office.

And though the plug-ins will also aid the state's effort to have 50 percent of its fleet made up of hybrids or other alternative-fuel vehicles by 2018, they are not necessarily the most cost-effective option on the market, especially as gas prices have fallen sharply in recent weeks. For that to happen, gas prices would have to soar to $6 a gallon, according to a study by Duke University researchers scheduled to be published next week.

Even so, Giudice said, the state has a responsibility to try out new environmentally friendly technology.

"They reduce emissions, they save energy, they reduce our dependence on oil," he said. And as more become available, Giudice added, such vehicles are likely to become less expensive.

Erin Ailworth can be reached at eailworth@globe.com.