to be derived from the Highway Trust Fund (other than the Mass Transit Account) and to remain available until expended: Provided, That funds available for the implementation or execution of motor carrier safety programs shall not exceed total obligations of $516,300,000 in fiscal year 2024 for Motor Carrier Safety Grants : Provided further, That of the amounts made available under this heading— (1) $406,500,000, to remain available for obligation until September 30, 2025, shall be for the motor carrier safety assistance program