The U.S. Secretary of Transportation is demanding information from the MBTA over safety concerns, threatening to withhold federal funding if the T fails to respond within two weeks. Secretary Sean Duffy, in a letter to MBTA Chief Phil Eng dated Thursday, cited the federal agency's "continued focus on ensuring safe travel in Boston" in seeking information about the T's "practices and expenditures." Duffy requested information on how the T plans to "reduce crime, vagrancy and fare evasion on the transit system." The press release said Duffy also sent a letter to the Chicago Transit Authority. Earlier this year, his office said, he sent similar letters to transit authorities in Washington, D.C., New York and Los Angeles.