Admittedly, I've never looked it up in the laws. It was in our drivers ed book in HS. I suppose maybe it's changed in the past 15 or so years. And I'm not at all advocating that people violate the vehicle code. I'm saying they should make sure they're giving the cyclist a reasonable warning that they're approaching from behind. In any case, all of the standard width road lanes are car, truck, bus, etc, lanes. They are. Get over it. As I said above, there's a reason they're 55mph and, surprise, the width of a car/truck, not a bike. And hey, they're researched, designed, and built for car/truck travel too. For some reason I've never once heard of them doing road testing to make sure it's suitable for cycling use. They do however do that for some lanes. Those are the bike lanes. I'm surprised you didn't notice the difference when you were in Madison, as there are plenty of bike lanes downtown for you to use as a comparison. You'll notice a significant difference between the two.

I'm All for biking, and I'm even for biking on roads that are safe and when it's a reasonable compromise for a biker to be there, but bikes should not be riding in the middle of a car lane, blocking traffic on a busy road, or be riding on a high mph road if it isn't a reasonable area for a car to safely go around them in the other lane. If they do, they're a self centered prick. It's also illegal to impede traffic, even if it's a cyclist. It's just one of those things that the cops never do anything about.

EDIT: Just did a quick google search on the horn honking. While it may not be "law," it looks like many states do advise giving a cyclist a honk to alert them that you are approaching/intend to pass.