This is the intersection of 2 one way streets in downtown Lansing.  While the detour signs seem to suggest that you can go in either directions, the street is one way going to the right.  Going to the left can be done if you have a whole lot of determination.

But more to the point, the detour sign pointing to the left is for pedestrians only.  Unfortunately,  most drivers do not pick up on that little bit of subtlety.

I sent this picture to a friend of mine in the highway department.  They changed the signage later that day.