The Obama administration is ready to let states break an old taboo: charge tolls on interstate highways to get money to repair and reconstruct them.It’s a worthy idea — at least as an added option for states strapped for cash and burdened by deteriorating interstates. Whether Texas should use that tool would be a separate debate for lawmakers in Austin.Transportation funding is tight everywhere.Since the federal interstate system was launched in 1956, tolls have generally been forbidden.The major exceptions have been roads that had tolls before they became interstates and, more recently, projects like the construction on Interstate 35W in Fort Worth that will add toll lanes while renovating the existing roadway.Congress can nix the president’s proposal, part of a $302 billion transportation bill unveiled by the Transportation Department on Tuesday. The main source of federal highway money, the Highway Trust Fund, is expected to run dry by August.The trust fund is fueled mainly by the federal gasoline tax of 18.4 cents per gallon and the diesel tax of 24.4 cents per gallon.Congress could raise those taxes, which it hasn’t done since 1993. The fund’s earnings have been eroded by more than 20 years of inflation, and revenue has been hurt as Americans drive less and own vehicles that are more fuel-efficient.Texas collects a tax of 20 cents per gallon on gasoline and diesel, a rate not changed since 1991. One-fourth of the revenue is diverted to help fund public education.Raising fuel tax rates is not popular in Washington or Austin. Still, interstates built to last 50 years are well past that, so toll revenue would be useful.Texans will vote in November on diverting about $1.2 billion a year in oil and gas severance taxes from the state’s rainy-day fund savings account to be used for transportation funding. State transportation officials say they need $4 billion a year just to keep traffic congestion from getting worse.