They reduce the booty collected by the state.
The state predicts gas tax collected today won't add up to enough cash to pay for future road projects.
Drivers of fuel-efficient cars are spending less at the pump, which means they are paying less in gas tax while driving the same amount of miles. So the state is a considering a pay-by- mile tax to even the playing field since as it stands now, drivers of gas guzzlers pay more in taxes per mile than drivers of fuel-efficient cars.
"In the future, as vehicles get more and more efficient, that puts a strain on our ability to maintain and operate our transportation system," said Jeff Doyle of the Washington state Department of Transportation.