; Public Law 110–53 ) is amended by inserting and associated backfill after security training . 613. 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 by striking subsection (m) and inserting the following new subsections: (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. (n) Authorization of appropriations There is authorized to be appropriated for grants under this section $200,000,000 for each of fiscal years 2021 through 2022. . 614. Comptroller General review of public transportation security assistance grant program (a) In general The Comptroller General of the United States shall conduct a review of the public transportation security assistance grant program under section 1406 of the Implementing Recommendations of the 9/11 Commission Act of 2007 ( 6 U.S.C. 1135