I tried it, so in case you wanted to do it too:
How exciting that there is a route that will go from where I was to where I wanted to be! As, I’m sure, with any long muti-state route, the conditions were quite varied. Sometimes two lanes, sometimes it was more, sometimes busy, some chunks very quiet, at times there was an awesome shoulder, and others none to speak of, sometimes it was even marked as a bike lane.
I had almost no trouble with drivers in Detroit. All the roads there were huge and most people seemed to have no problem using a different lane than the one I was in. Not as much in the immediate suburbs. But, it wasn’t too bad. For the most part in rural areas I was not bothered, though I was probably passed closely by trucks a few more times than ideal.
As I approached Ypsilanti 12 splits and there is the option to take Business 12. This is the right choice, which I did not make. 12 then merges with I-94. I was surprised by this. Don’t panic, it worked out ok. I got off at the next exit and had to do some guessing and some backtracking and eventually got back on route, but it meant going east a ways to get on the west bound again.
I had a day of going in the right direction, through largely rural Michigan. Then you get to Niles and it suddenly turns and becomes a four lane only motor vehicles highway… just for a little bit, you know? So I stopped in a gas station… the detour is simply go a few miles north up to the center of Niles where you can cross the river, then come back south to get back on 12. I found a spoon. (I have a collection of flatwear I’ve found in the road, various states of mangled, I picked up five things in Michigan and saw two that I let go. If I mention finding things, this is what I’m talking about.)
12 goes almost up to the shore of Lake Michigan, through many little lakeside towns, through the Indiana Dunes National Lakeshore Park. It gets a little confusing as you get closer to Chicago, it was and was not the same path as US 20 for bits, sometimes only one would be marked for a stretch which made me feel confused (it may not have if I had looked well at a map ahead of time).
It got big and busy (though not illegal to be on as far as I could tell) south of Chicago and I ditched it for a bike path when it was offered to me- we saw each other a couple times after that, but it is definitely over between us for now.