Mich. Comp. Laws § 28.8

Sec. 8. The grades and duties of the officers of the department are colonel, lieutenant colonel, major, captain, inspector, lieutenant, sergeant, trooper, and recruit. The officers may carry arms either openly or concealed. Every member of the department is subject to orders at any time, and the officers of the department at all times have the authority to apprehend criminals and preserve law and order. When traveling on duty, officers and civilian employees of the department are entitled to transportation on any railroad, passenger steamboat line, airline, or passenger bus line upon presentation of a requisition for the transportation signed by the director of the department and those carriers are entitled to compensation for transportation furnished out of money appropriated for the department.