appropriations for fiscal year 2021, $16,595,000,000, to be derived from the Mass Transit Account of the Highway Trust Fund and to remain available until expended: Provided , That funds available for the implementation or execution of programs authorized under 49 U.S.C. 5305 , 5307, 5310, 5311, 5312, 5314, 5318, 5329(e)(6), 5335, 5337, 5339, and 5340, as amended by the Fixing America's Surface Transportation Act, section 20005(b) of Public Law 112–141 , and section 3006(b) of the Fixing America's Surface Transportation Act, or any successor surface transportation reauthorization Act authorizing appropriations for fiscal year 2021, shall not exceed total obligations of $15,945,200,000 in fiscal year 2021: Provided further , That the Federal share of the cost of activities carried out under 49 U.S.C. section 5312 shall not exceed 80 percent, except that if there is substantial public interest or benefit, the Secretary may approve a greater Federal share: Provided further , That until September 30, 2021, for amounts subject to the obligation limitation under this heading during fiscal year 2021, the Federal share of costs for any grant made for activities undertaken pursuant to chapter 53 of title 49, United States Code, shall be, at the option of the recipient, up to 100 percent but solely for funds that have not been obligated to a grant prior to September 30, 2020: Provided further , That the preceding proviso shall not apply to grants made pursuant to a competitive application process in fiscal year 2021 or any prior fiscal year: Provided further , That not including any amounts provided under the heading Transit Infrastructure Grants in title XII of division B of the CARES Act ( Public Law 116–136 ), an urbanized area or State may obligate not more than 50 percent of its unobligated balances authorized under sections 5305, 5307, 5310, 5311, 5329(e)(6), 5335, 5337, 5339, and 5340 of title 49, United States Code, as of September 30, 2020, under this proviso. Transit infrastructure grants For an additional amount