(a) An SHA that uses the proceeds of bonds issued by the State, a county, city or other political subdivision of the State, for the construction of projects on the Federal-aid primary or Interstate system, or extensions of any of the Federal-aid highway systems in urban areas, or for substitute highway projects approved under 23 U.S.C. 103(e)(4), may claim payment of any portion of such sums apportioned to it for expenditures on such system to aid in the retirement of the principal of bonds at their maturities, to the extent that the proceeds of bonds have actually been expended in the construction of projects.

(b) Any interest earned and payable on bonds, the proceeds of which were expended on Interstate projects after November 6, 1978, is an eligible cost of construction. The amount of interest eligible for participation will be based on (1) the date the proceeds were expended on the project, (2) amount expended, and (3) the date of conversion to a regularly funded project. As provided for in section 115(c), Pub. L. 95-599, November 6, 1978, interest on bonds issued in any fiscal year by a State after November 6, 1978, may be paid under the authority of 23 U.S.C. 122 only if such SHA was eligible to obligate Interstate Discretionary funds under the provisions of 23 U.S.C. 118(b) during such fiscal year, and the Administrator certifies that such eligible SHA has utilized, or will utilize to the fullest extent possible during such fiscal year, its authority to obligate funds under 23 U.S.C. 118(b).

(c) The Federal share payable at the time of conversion, as provided for in § 140.610 shall be the legal pro rata in effect at the time of execution of the project agreement for the bond issue project.

(d) The authorization of a bond issue project does not constitute a commitment of Federal funds until the project is converted to a regular Federal-aid project as provided for in § 140.610.

(e) Reimbursements for the redemption of bonds may not precede, by more than 60 days, the scheduled date of the retirement of the bonds.

(f) Federal funds are not eligible for payment into sinking funds created and maintained for the subsequent retirement of bonds.