30 ILCS 105/5d
Except as provided by Section 5e of this Act, the State Construction Account Fund shall be used exclusively for the construction, reconstruction and maintenance of the State maintained highway system. Except as provided by Section 5e of this Act, none of the money deposited in the State Construction Account Fund shall be used to pay the cost of administering the Motor Fuel Tax Law as now or hereafter amended, nor be appropriated for use by the Department of Transportation to pay the cost of its operations or administration, nor be used in any manner for the payment of regular or contractual employees of the State, nor be transferred or allocated by the Comptroller and Treasurer or be otherwise used, except for the sole purpose of construction, reconstruction and maintenance of the State maintained highway system as the Illinois General Assembly shall provide by appropriation from this fund. Beginning with the month immediately following the effective date of this amendatory Act of 1985, investment income which is attributable to the investment of moneys of the State Construction Account Fund shall be retained in that fund for the uses specified in this Section.
30 ILCS 105/5d