Michigan Compiled Laws, Chapter 257. Motor Vehicles § 257.601a

Sec. 601a. (1) A county, city, township, or village may contract with a person who owns or is in charge of a private road that is open to the general public, at that person's request or with that person's consent, to enforce provisions of this act on that private road.

(2) Subject to subsection (1) and section 906,  1 a peace officer may enter upon a private road that is open to the general public to enforce provisions of this act if signs meeting the requirements of the Michigan manual of uniform traffic control devices are posted on the private road.

(3) The owner or person in charge of a private road open to the general public who enters into a contract as described in subsection (1) is responsible for the cost and the posting of signs described in subsection (2).

(4) This section does not affect a contract entered into between a county, city, township, or village and the person who owns or is in charge of a private road open to the general public before December 29, 2006.

(5) As used in this section, “private road that is open to the general public” does not include a road that is under the control of a mobility research center, regardless of whether a private research entity or a corporation is using the road under an agreement with the mobility research center.