Some cities in Europe have so many roundabouts, and two or three lane roundabouts with complex exit decisions you need to make on a split second - it's actually very confusing to navigate.
Agree, when at or near 100% utilisation, its slower than a normal junction.
> you may actually increase the risk of collision due to negotiations about right of way happening every time a car can move forward.
That shouldn't be the case. Ideally you should always have priority from one direction (like in the UK, germany and the netherlands.) The generally rule is that when you come to the round about, if you see someone on your right(in the UK, left everywhere else I imagine) you stop and wait for them to drive past.
> two or three lane roundabouts with complex exit decisions you need to make on a split second
The driving exam will test you for this in the EU. The lane you chose is directly related to where you need to exit. If you are going straight over, or less, then its the outer most lane. Anything more than 180 degrees you take the inner lane. Exceptions will be clearly marked in both floor markings and signs well before entry.
and two or three lane roundabouts with complex exit decisions you need to make on a split second - it's actually very confusing to navigate.
I think you're confusing what today might be called a "rotary" (?) with a modern roundabout. Whatever you call it, I don't think anyone builds what you're describing anymore.
They decrease serious collisions.
Because they don't remove the idiots from the roads. The same people who willfully ignore right of way at stops signs also ignore right of way in the roundabout.