625 ILCS 5/20-101
From and after the effective date of this Act, except as provided in Section 3-815.1 of this Code, no public moneys derived from fees, excises or license taxes relating to registration, operation and use of vehicles on public highways or to fuels used for the propulsion of such vehicles, shall be appropriated or expended other than for costs of administering the laws imposing such fees, excises and license taxes, statutory refunds and adjustments allowed thereunder, administrative costs of the Department of Transportation, payment of debts and liabilities incurred in construction and reconstruction of public highways and bridges, acquisition of rights-of-way for, and the cost of construction, reconstruction, maintenance, repair and operation of public highways and bridges under the direction and supervision of the State, political subdivision or municipality collecting such moneys, and the costs for patrolling and policing the public highways (by the State, political subdivision or municipality collecting such money) for enforcement of traffic laws; provided, that such moneys may be used for the retirement of and interest on bonds heretofore issued for purposes other than the construction of public highways or bridges but not to a greater extent, nor a greater length of time, than is provided in acts heretofore adopted and now in force. Further the separation of grades of such highways with railroads and costs associated with protection of at-grade highway and railroad crossings shall also be permissible.
625 ILCS 5/20-101