SALT LAKE CITY -- Federal highway regulators are giving their approval for electronic tolling for express lanes along a stretch of Interstate 15.

U.S. Transportation Secretary Mary Peters signed off on the plan in Salt Lake City.

What's more, Peters said Monday that states shouldn't have to even ask federal permission to bill tolls electronically.

Utah is spending its own money to make the switch, but it took months and a lot of red tape for the Utah Department of Transportation to get federal approval, she said.

Peters said she was lending support to a Bush administration proposal to delegate more decisions on interstate operations to states and metropolitan transportation authorities. The same proposal would limit Congress' ability to dole out so-called earmarks for favorite local projects.

"Under our approach, cities will no longer have to slice and dice every federal dollar to qualify for niche programs that do little to improve communities or their commutes," Peters said. "Instead, projects that improve commutes, give taxpayers a good deal and cut congestion get funding."

The I-15 express lanes run for 38 miles along the Wasatch Front. Soon, they'll stretch for 76 miles.

The express lanes are reserved for motorists with at least one passenger or a low-emission car -- or people who pay $50 a month for the right to use them.

Utah wants to vary billing rates according to the time of day and amount of traffic by using a microchip installed in cars.

UDOT wants to give motorists an incentive to alter their driving schedules to take advantage of cheaper tolls at off-peak hours to ease traffic congestion.

"This system will be a major part of our future," said Carlos Braceras, the department's deputy director. "Now, some people think that their use of the road is free, but they're forgetting they pay the gas tax. By making people aware of the costs to use the road and the express lanes, we're hoping to spread peak congestion and save people time and money."