Maui Mayor Charmaine Tavares is test-driving a plug-in hybrid vehicle to promote cutting back on fossil fuel consumption.

The converted Toyota Prius is part of a national study run by the Idaho National Laboratory and the U.S. Department of Energy. The survey has cars in a variety of geographic locations to test how they do in different environments.

In April, the first month, Tavares' test car averaged 64 miles per gallon. Maui Electric also has a car, while there are four more on O'ahu, including one used by Hawaiian Electric Co.

Like conventional hybrid cars, Tavares' converted Prius recharges its battery when the driver brakes. But the vehicle also contains an additional battery pack that can be recharged at an ordinary electrical outlet.

This allows the car to use less gasoline. It also lets the vehicle harness wind, solar, and other clean, renewable energy resources collected by Maui Electric Co.

Tavares is driving Maui's test vehicle to give renewable energy use maximum exposure, said Victor Reyes, Maui's energy commissioner. "She's really a champion for this," Reyes said.