1. Short title This Act may be cited as the Transit Security Grant Program Flexibility Act . 2. Allowable uses of funds for public transportation security assistance grants Subparagraph (A) of section 1406(b)(2) of the Implementing Recommendations of the 9/11 Commission Act of 2007 ( 6 U.S.C. 1135(b)(2) ; Public Law 110–53 ) is amended by inserting and associated backfill after security training . 3. Periods of performance for public transportation security assistance grants Section 1406 of the Implementing Recommendations of the 9/11 Commission Act of 2007 ( 6 U.S.C. 1135 ; Public Law 110–53 ) is amended— (1) by redesignating subsection (m) as subsection (n); and (2) by inserting after subsection (l) the following new subsection: (m) Periods of performance (1) In general Except as provided in paragraph (2), funds provided pursuant to a grant awarded under this section for a use specified in subsection (b) shall remain available for use by a grant recipient for a period of not fewer than 36 months. (2) Exception Funds provided pursuant to a grant awarded under this section for a use specified in subparagraph (M) or (N) of subsection (b)(1) shall remain available for use by a grant recipient for a period of not fewer than 55 months. . 4. GAO review (a) In general The Comptroller General of the United States shall conduct a review of the transit security grant program under section 1406 of the Implementing Recommendations of the 9/11 Commission Act of 2007 ( 6 U.S.C. 1135