; (ii) payments owing to the obligor under a public-private partnership; or (iii) other dedicated revenue sources that also secure the senior project obligations; and (B) include a coverage requirement or similar security feature supporting the project obligations. (4) Interest rate (A) In general Except as provided in subparagraph (B), the interest rate on a secured loan under this section shall be not less than the yield on United States Treasury securities of a similar maturity to the maturity of the secured loan on the date of execution of the loan agreement. (B) Limited buydowns (i) In general Subject to clause (ii), the Secretary may lower the interest rate of a secured loan under this section if the interest rate has increased between the period— (I) beginning on, as applicable— (aa) the date on which an application acceptable to the Secretary is submitted for the applicable project; or (bb) the date on which the Secretary entered into a master credit agreement for the applicable project; and (II) ending on the date on which the Secretary executes the Federal credit instrument for the applicable project. (ii) Limitation The interest rate of a secured loan may not be lowered pursuant to clause (i) by more than the lower of— (I) 1 1/2 percentage points (150 basis points); and (II) an amount equal to the amount of the increase in the interest rate described in that clause. (5) Maturity date The final maturity date of the secured loan shall be the earlier of— (A) the date that is 35 years after the date of substantial completion of the project