Plaque on the Overpass

I'm taking a walk late last month, and I come upon this plaque on an overpass crossing the Lodge Freeway (M-10) in downtown Detroit. I've noticed them for a while, and after reading them, I saw that these were plaques that said that these were constructed by the authority of the State and County Highway Departments and the city. This bridge in particular was built in the early 1950s. The freeway was built in the 1950s, and is one thoroughfare from downtown into the suburbs. There are a couple of bus routes that travel the Lodge during rush hours during the week. There are more plaques along the freeway like this one. Many, if not all, are greened (they were originally Bronze) due to time and the elements.