PORTLAND, Ore., March 25 (UPI) -- Oregon is testing the idea of collecting highway funds through a tax on miles driven, rather than gasoline consumed.

Eighty percent of Oregon's highway money comes from its 24-cents-per-gallon gas tax. If the state promotes reducing gasoline consumption and consumers tend to buy the fuel-efficient vehicles, including hybrids, highway revenues would take a hit, The New York Times reported.

The test program uses a global positioning system to track miles driven, using a black box to calculate how many miles are clocked in-state, out of state and during rush hour.

The experiment is designed to increase state revenue for road maintenance without raising gasoline taxes, but critics say collecting GPS records poses new privacy issues.

"The existence of such a database, which would, for the first time in history, allow for the creation of detailed daily itineraries of every driver, raises obvious privacy concerns," said David L. Sobel, general counsel at the Electronic Privacy Information Center, a civil liberties group in Washington.