[0] https://www.google.com/maps/place/Energieweg,+Nijmegen/@51.8...
You're not wrong, but roundabouts degraded the busier they get:
> As at other forms of unsignalized intersection, when traffic flows on an approach exceed approximately 85 percent of capacity, delays and queue lengths vary significantly about their mean values (with standard deviations of similar magnitude as the means). For this reason, the analysis procedures in some countries (Australia, Germany, and the United Kingdom), and this guide, recommend that roundabouts be designed to operate at no more than 85 percent of their estimated capacity.
* https://www.fhwa.dot.gov/publications/research/safety/00067/...
1-, 2-, and 3-lane RAs each have different capacities, and it may not be easy to expand one size to the next larger one depending on what else is in the area, so signals can allow for the general architecture of RAs to be extended without major changes besides putting up some poles and wires.
In the UK there are road markings that indicate a similar flow, but this turboroundabout makes it physical.
* Raised curbs force the outside lane to exit.
* After each exit, there are only 2 lanes left.
* After each entry, there are 3 lanes, a new one starts from scratch on the inside.
That said, my recollection is that the default in the UK is that lanes flare out from the center, so that once you get into the lane you don't have to switch to another to exit.