In Michigan, bicyclists are instructed to take the lane whenever riding on the road. Shoulder riding is an option, but never, ever required, much like sidewalk riding, due to the dangers and poor maintenance (michigan roads are terrible, but their sidewalks and shoulders are even worse). One cyclist is instructed to be at minimum 2 feet from the edge of the road, in the position a car's right tire would be or thereabouts, to discourage cars from unsafely passing *without* crossing into the passing lane. Bicyclists on the road are meant to be treated as cars in all respects. Two abreast riding is totally allowable as well (but not more), with in that situation the second bike riding where the left wheel would be. They do ask that when it is safe to pass you switch to one abreast to signal that to drivers and make it easier for them. My point being that when one person is on the shoulder, in Michigan that means you could have one on shoulder, and two on the road, and completely take up the traffic lane, and that would not only be totally legal, but complying with the advisements of Michigan's DOT. So no, it's not obstructing traffic. As someone else aptly said, bicyclists don't obstruct traffic, they *are* traffic.

I learned the hard way to care more about my safety than drivers convenience when I was riding on the sidewalk and since drivers pay no attention I got hit by someone turning into a parking lot (when on sidewalks, bikes are meant to be treated as pedestrian traffic, but he wasn't looking regardless and would have hit me had I been a pedestrian as well). So if I have to be dead center in the traffic lane wearing 100% reflective gear for cars to notice me, so be it. Cars that can't handle that and wait until they can safely pass, shouldn't be on the road, and if they "squeeze" past, tail incredibly close, or do other unsafe and aggressive maneuvers, they get reported to the police, with possible criminal charges attached for reckless endangerment, assault with a deadly weapon, or similar, and likely won't be on the road in the future.