WASHINGTON — The Transportation Department asked Congress on Tuesday to end the prohibition on tolling existing interstates as a way to pay for their reconstruction, marking a major shift away from how the system has been funded for decades.The proposal is part of President Barack Obama’s $302 billion infrastructure bill to address a looming shortfall in the Highway Trust Fund. States can toll interstates only if they’re adding lanes, but many simply don’t have the money to widen or rebuild the oldest sections of interstate. Neither does the federal government.Transportation Secretary Anthony Foxx said Tuesday that the Highway Trust Fund is set to run out of cash in August, a scenario that would hurt most states. According to the American Road and Transportation Builders Association, a trade group, 31 states rely on federal funds for more than half their highway and bridge improvements.McClatchy reported two years ago that three states — Missouri, North Carolina and Virginia — were considering tolls to rebuild their oldest interstates under a federal pilot program limited to three applicants. None of the states have enacted tolling, but Tuesday’s proposal would grant that option to every state.Longtime advocates of expanded tolling lauded the proposal. Pat Jones, executive director and CEO of the International Bridge, Tunnel and Turnpike Association, noted that 35 states have used tolling as a “proven and effective option” for infrastructure improvements.Still, the trucking industry and motorist groups renewed their opposition Tuesday. Toll opponents argue that payment collection systems are inefficient, that they raise costs for businesses and consumers, and that they divert traffic to local roads that were never designed for high traffic volumes.The trucking industry and the U.S. Chamber of Commerce support increasing federal taxes on gasoline and diesel fuel, though the White House and Congress have shown little appetite for that. Bill Graves, president and CEO of the American Trucking Associations and a former Republican governor of Kansas, called the administration’s plan “disappointing.”“The focus must be on real, long-term funding answers rather than repeatedly looking for the proverbial ‘nickels in the couch cushions,’ ” Graves said.