State Transportation Flexibility Act This bill allows a state to elect not to participate in the federal-aid highway program, including any federal highway program under the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users, the Moving Ahead for Progress in the 21st Century Act, or the Fixing America's Surface Transportation (FAST) Act. The Department of Transportation (DOT) shall carry out a direct federal-aid highway program to permit a state legislature, at least 90 days before the beginning of a fiscal year, to elect to: waive the state's right to receive apportioned or allocated funds under the federal-aid highway program, and receive a prorated amount of taxes appropriated to the Highway Trust Fund (other than for the Mass Transit Account) which are attributable to highway users in the state. The state making an election shall: agree to maintain the Interstate System in accordance with the current Interstate System program; submit a plan describing the purposes, projects, and uses to which such amounts will be put and the federal-aid highway programmatic requirements the state elects to continue; agree to obligate or expend program amounts exclusively for projects that would be eligible for surface transportation program funding; and. agree to report annually to DOT on the use of amounts received under the program and to make the report publicly available. DOT shall carry out a similar alternative funding program for public transportation programs.