Mich. Comp. Laws § 124.557

Sec. 17. The costs of planning, administering, constructing, reconstructing, financing, and maintaining state, county, city, and village roads, streets, and bridges designed primarily for the use of motor vehicles using tires, including the costs of reasonable appurtenances to those state, county, city, and village roads, streets, and bridges, are a transportation purpose within the meaning of section 9 of article IX of the state constitution of 1963, when such costs are to facilitate a public transportation system that moves individuals or goods with vehicles using tires.