49 U.S.C. § 44307 — Revolving fund

(a) Existence, Disbursements, Appropriations, and Deposits. (1) There is a revolving fund in the Treasury. The Secretary of the Treasury pays out of this fund to carry out this chapter. (2) Congress may appropriate the money this chapter needs into the fund. Appropriated amounts, and other money received while carrying out this chapter, go into the fund. (b) Investment. At the Secretary of Transportation's request, the Secretary of the Treasury may invest part of the fund in interest-bearing U.S. government securities. The interest, and any proceeds from selling or redeeming those securities, go back into the fund. (c) Excess Amounts. Whatever balance the fund holds beyond what the Secretary of Transportation decides it needs — including reasonable reserves to keep the fund solvent — must be deposited into the Treasury at least once a year, as miscellaneous receipts. (d) Expenses. Each year, the Secretary of Transportation must deposit into the Treasury, as miscellaneous receipts, an amount covering the government's expense from the Secretary using appropriated money under this chapter. That amount equals the fund's average monthly balance of appropriated money, multiplied by a percentage that is at least the current average rate on marketable government obligations. The Secretary of the Treasury sets that percentage each year, in advance.