Mich. Comp. Laws § 254.327
It is hereby found, determined and declared that the creation of the authority and the carrying out of its corporate purposes are in all respects for the benefit of the people of the state and constitute a public purpose, and that the bridge is an essential part of the public highway system of the state and that the authority will be performing an essential governmental function in the exercise of the powers herein conferred upon it. Therefore, all property owned by the authority hereunder shall be exempt from all taxes levied by the state of Michigan and all of its political subdivisions and taxing districts, and the authority shall be required to pay no taxes or assessments upon its activities or upon any of its revenues. If at any time hereafter any taxes of any nature shall be legally imposed on any properties of the authority or the obligations thereof, and such taxes shall be determined to be valid and effective, they shall be paid from the revenues of the authority as 1 of the expenses of maintaining and operating the bridge.
MCL 254.327