Mich. Comp. Laws § 252.57
The state highway commissioner and any county, city or village, after approval of the plans and specifications and estimate of cost as aforesaid, may enter into a contract or contracts providing for the acquisition, construction or improvement of the limited access highways proposed, which contract or contracts shall provide for the allocation of the share of the cost thereof to be borne by each of said governmental units and provide for the payment of the share of the cost thereof to be borne by each such governmental unit in annual installments for a period of not exceeding 30 years. Such contract or contracts shall be executed by the state highway commissioner, after approval thereof by resolution of the state administrative board, and by the board of county road commissioners of each contracting county, subject to the approval of the board of supervisors, and by each city or village, pursuant to resolution of their respective legislative bodies.
MCL 252.57