A quick google search shows that the Michigan Constitution requires money to be used for Transportation purposes
Act 51 - then dictates how that money is spent:
Article IX, Section 9, of the Michigan Constitution of 1963, as amended, states that "All specific taxes . . . imposed directly or indirectly on fuels sold or used to propel motor vehicles upon highways. . . or on registered motor vehicles . . . shall, after payment of necessary collection expenses, be used exclusively for transportation purposes. . ." Public Act 51 of 1951, as amended ("Act 51") governs the distribution of this revenue. The following pages summarize this distribution. Act 51 creates a fund into which specific transportation taxes are deposited, and prescribes how these revenues are to be distributed and the purposes for which they can be spent. Act 51 establishes jurisdictional road networks, sets priorities for the use of transportation revenues, and allows bonded indebtedness for transportation improvements and guarantees repayment of debt.
https://www.michigan.gov/documents/act51simple_28749_7.pdf
How does Michigan get away with violating the constitution and state code?