DAVIS, Calif. --- For the next two years, a research team at the University of California at Davis will study driver attitudes and preferences about plug-in hybrids. Ten modified Toyota Priuses, which can be recharged from a 110-volt electric outlet, will be loaned to 100 families in northern California for six to eight weeks each. The drivers will be surveyed about their automobile preferences and attitudes before, during and after they use the cars. The U.C. Davis analysis of their experiences will constitute the first comprehensive consumer report on plug-in hybrid electric vehicles. The cars can travel as far as 20 miles on batteries before drinking a drop of gasoline, or get 100 miles per gallon in combined gasoline-electric mode. "What we have seen is that, as consumers become more aware of hybrids, the cars are going beyond the innovators to the core market. The Prius is now the best-selling sedan in the San Francisco Bay Area and one of the most popular cars in California," said Tom Turrentine, a research anthropologist at the U.C. Davis Institute of Transportation Studies. He directs the university's new Plug-in Hybrid Electric Vehicle Research Center. Plug-in hybrids, however, are still virtually unknown to consumers. There are fewer than 100 plug-in hybrids in the U.S. today. All are cars that were converted by their owners, since there are no commercially produced plug-ins for sale yet. With so few on the road, little is known about how consumers will use them. Policymakers, energy suppliers and automakers are asking UC Davis to fill in some of the blanks. "We know that existing hybrids offer environmental benefits and some savings on fuel costs," said Turrentine. "Plug-in hybrids offer improvements of those benefits, plus the ability to recharge at home and choice of fuel alternatives. It's your choice every day -- you can choose to use electricity or you can choose to use gasoline." What is the difference between a conventional hybrid and a plug-in? Hybrids are powered by a combination of electricity and gasoline, but are never plugged in. The electricity they use is generated "on board" when the driver steps on the brakes. Plug-in hybrids have bigger batteries to store more electricity, and can be plugged into the electricity grid for recharging. Designs vary, but some plug-in hybrids can operate on electricity alone for distances as long as 40 miles. Plug-ins are less expensive to run, at about 2.7 cents per mile in electric-only mode, compared with 7 cents per mile for a conventional hybrid (and 10 cents per mile for an average gasoline-only car). Moreover, while driving a hybrid reduces consumption of fossil fuel for transportation, driving a plug-in hybrid reduces it even more, by using less gasoline or diesel and more electricity. The U.C. Davis Plug-in Hybrid Center was established in January with $3 million in funding from the California Energy Commission's Public Interest Energy Research (PIER) program. The consumer-attitude research project is supported with an additional $1.8 million from the California Air Resources Board. Two other key partners in the Plug-in Hybrid Center are Pacific Gas & Electric Co. and the American Automobile Association of Northern California.