Roundabouts are great, as long as you do not get a timid driver at the head of the queue!
What I have found, in rush hour traffic, is one lane moves faster than the other, so all the flyboys jump into that. It then comes to a halt, the other lane speeds up, and they all dodge back. I pick a lane and stick to it, and seldom find, when the traffic again flows freely, that I am more than four vehicles behind or ahead of the car I started beside.