> They are so common, they work so poorly even when everybody knows what they're doing, and nobody ever knows what they're doing with them.
4 way stops are just evil. Where I live, nobody comes to a full stop (even though think they think they do), and because the danger is a little less than a full intersection with a traffic light, people will go out of turn because they think their time is worth more than everyone else's.
I think it's interesting to analyze these things in terms of how many different things you have to pay attention to.
With a roundabout, you need to look to the left (or right, for those in the appropriate countries) for oncoming traffic in the roundabout, and yield to it. You also need to check your entrance's crosswalk for pedestrians, and wait for them. Separately, when you exit, you also have to check that crosswalk for pedestrians, and wait for them. In total, you have to pay attention to two things as you enter, and then separately one thing as you exit.
With a four-way stop, you have to check all three other entrances when you arrive. You must also check your crosswalk, of course. You must also simultaneously check your destination crosswalk, since it's simply not reasonable to wait for pedestrians while in the middle of the intersection. You also have to check both other crosswalks, because pedestrians there can influence what the cars there will do. Thus there are a total of seven different things you must all check simultaneously to make it through a four-way stop.
4 way stops are just evil. Where I live, nobody comes to a full stop (even though think they think they do), and because the danger is a little less than a full intersection with a traffic light, people will go out of turn because they think their time is worth more than everyone else's.