Michigan Left

[talindsay]

I could have put this in "transportation" but thought it would be better here. Mods, feel free to move if you think it belongs in transportation.

So I was in Ann Arbor for work this week and encountered one of the oddest intersection engineering solutions I've seen, the Michigan Left:

http://www.michiganhighways.org/indepth ... _left.html
https://en.wikipedia.org/wiki/Michigan_left

They do work fairly well but introduce some odd problems, such as the need for left-turning traffic to cross all lanes of the counter-direction traffic flow to get to the U-turn point for their direction.

What I find most interesting (and odd) is that in their defense of the "Michigan Left" the Michigan highway department shows all sorts of numbers about how much safer and faster they are than traditional four-way intersections, but they don't say anything about how they compare to roundabouts. It seems to me that it's trying to solve the same problem as a roundabout, and doing it in a much less elegant fashion. I can see that it has some benefits over a roundabout when the two roads are of vastly unequal traffic volume, but elongated roundabouts can often handle even that situation quite well; also, the Michigan Left still relies on traditional traffic signals for the through traffic unless the secondary road is truly very secondary.

Anyway, I thought it was interesting and I'll ponder the design a bit longer but my initial reaction is that while it may help in some situations, most of the time a roundabout would solve the issues better that might cause one to consider changing an intersection in the first place.

[MNdible]

My gut is that a roundabout makes more sense when the different "spokes" have more or less equal traffic. When one cross street has much heavier volumes than the other, a roundabout might makes less sense and a solution like this may be more appropriate.

[mattaudio]

Similar in concept, but preventing through movement on the smaller road:
http://www.dot.state.mn.us/roadwork/rci.html

Also, I like the idea of using our street grid to serve this function on streets where left turning cars create excessive conflict... solution to the northbound-cars-left-hooking-northbound-cyclists issue on the proposed Minnehaha cycletrack?

[Nathan]

Ugh, they are sooo awful. My sister lives just north of Detroit. If you don't know what is going on it totally screws you up. Exiting the interstate to go different directions have different exits, and if you wanted to go left, but you used the right turn one, there isn't an option to go left... it's SO much more infrastructure, as well. Roundabouts are way more compact and take up less space. You have to drive so much further to make that U turn, then come back and cross multiple lanes of traffic to go right. Just my personal experience...