; (2) for which construction began on or after October 1, 2018; and (3) that remains under construction as of June 1, 2023. (c) Funding limitations A grant provided under this section may not exceed $10,000,000. (d) Unused amounts Any funds not made available pursuant to this section shall be retained in the account to which the funds were appropriated and made available for any other purpose provided for by law. (e) Definitions The definitions in section 5309(s)(9) of title 49, United States Code, shall apply to this section. 5. Implementation The Secretary of Transportation shall implement the requirements of the amendments made by sections 2 and 3 of this Act not later than 270 days after the date of enactment of this Act.