Hybrids could pay more gas tax / U.S. to study tariffs on miles driven, not gallons purchased

Hybrids could pay more gas tax / U.S. to study tariffs on miles driven, not gallons purchased: "David Hamilton, national director of the Sierra Club's global warming and energy program, was more emphatic. 'If some vehicles use much more gas per mile, you are giving them an advantage by going to a per-mile charge, and that goes in exactly the wrong direction in helping to solve global warming and other environmental issues,'' he said. "