(1)
(a) All moneys resulting from the contracting of public debt shall be credited to a separate and distinct fund, established in the state treasury, designated as the capital improvement fund, except that such moneys which represent premium and accrued interest on bonds or notes issued, or are for purposes of funding or refunding bonds pursuant to s. 18.06 (5) shall be credited to one or more of the sinking funds of the bond security and redemption fund or to the state building trust fund.
(b) Moneys within the capital improvement fund shall be segregated into separate and distinct accounts according to the program purposes defined under ch. 20 for which public debt has been authorized by the legislature.
(2) The capital improvement fund may be expended, pursuant to appropriations, only for the purposes and in the amounts for which the debts have been contracted, for the payment of principal and interest on loans or on notes, for the purposes identified under s. 20.867 (2) (v) and (4) (q) and for expenses incurred in contracting debt.
(3) Moneys of the capital improvement fund may be commingled only for the purpose of investment with other public funds, but they shall be invested only as provided in s. 18.04 (6) or 25.17 (3) (b) . All such investments shall be the exclusive property of the fund and all earnings on or income from such investments shall be credited to the fund and shall, subject to subs. (5) and (6) , become available for any of the purposes under sub. (2) . Before October 1, 1983, earnings from that portion created by self-amortizing projects may be transferred by resolution of the commission to the bond security and redemption fund to be used as provided in s. 18.09 (4) .
(4) If at any time it appears that there will not be on hand in the capital improvement fund sufficient moneys for the payment of principal and interest on loans or on notes, the department of administration shall transfer to such fund, out of the appropriation made pursuant to s. 20.866 , a sum sufficient which, together with any available money on hand in such fund, is sufficient to make such payment.
(5) Before October 31, 1983, there shall be transferred to the bond security and redemption fund the interest earnings accrued to the capital improvement fund before October 1, 1983 due to the investment of moneys from the contracting of public debt under s. 20.866 (2) (u) to (uv) . These funds shall be used for meeting periodic principal, interest and premiums due, if any, on principal repayment and interest payments required from the transportation fund on this public debt.
(6) Before October 31, 1983, there shall be transferred to the bond security and redemption fund the interest earnings accrued to the capital improvement fund before October 1, 1983, due to the investment of moneys from the contracting of public debt under s. 20.866 (2) (tm) to (to) . These funds shall be used for meeting periodic principal, interest and premiums due, if any, on principal repayment and interest payments required from the general fund on this public debt.