REUTERS SUMMIT:Calif's Boxer sees future for gas tax, mile fees

By Lisa Lambert and John Crawley

WASHINGTON (Reuters) - The U.S. Senate is considering a wide variety of funding options for the country's roads, bridges and public transit as it drafts its version of a sweeping national transportation spending bill, Senator Barbara Boxer told Reuters on Thursday.

But it will not scrap the tax on gasoline sales, the primary source for highway funds, said the California Democrat, who will marshal the bill through the Senate.

"What I think is very important is to index the gas tax to inflation, because, obviously the gas tax is falling behind," she said at the Reuters Infrastructure Summit. "I also don't want to increase the gas tax, but I want it to keep up."

Last summer gas tax revenues dropped because drivers stayed off the roads as oil prices spiked, which depleted the trust used for highway construction and repairs.

The federal government refilled the fund, but the money will likely run out again by September, when the current transportation law expires. Congress must either pass a new spending bill or an extension of the current law.

Boxer said she was confident the bill would pass out of the Environment and Public Works Committee that she chairs and reach the full Senate by the end of the year.

The Senate is also considering raising the tax on diesel, changing exemptions to the gas tax given to certain groups, taking a percentage of customs duties, relying on private finance, and charging drivers fees based on Vehicle Miles Traveled, she said.

The bill's authors, though, have rejected attaching a small device to cars to measure Vehicle Miles Traveled, Boxer said.