[gnosek]

If I understand correctly, you mean turbo roundabouts https://www.ms2soft.com/resources/turbo-roundabouts/ ?

If so, IMO they're the best thing that happened to roundabout design ever. You do need to choose a lane before entering but it's similar to how you'd choose a lane on a traditional two-lane roundabout. However, then you don't change lanes while on the roundabout, with ~zero visibility to the other lane while turning in a fairly tight circle.

This may differ across countries but around here you're supposed to: * pick the inner lane unless you're taking the first exit (to the right) * change to the outer lane just before your exit

which is about infinity times more stressful in traffic (you have very little time, it's hard to see the outer lane and the outer lane has right of way). It would work fine if everybody followed the rules but 1. they don't since it's unsafe in a tragedy of the commons sort of way and 2. then you end up with an informal turbo roundabout anyway.

A compromise that's becoming fairly common is a "soft" turbo roundabout where the lanes are divided not by ridges but by solid lines you can't cross only legally, not physically :)

[consp]

Turbo roundabouts also have a significant bonus in throughput, have significantly less points of conflict than a normal two lane at the expense of longer lead-in roads. A single lane is safer but has a drawback in cars per hour.

[rapnie]

Thank you for the name. Yes, that design. As I just commented below the stress point shifts to entering the roundabout where people crazily yank their car sideways to be on the proper lane. At all cost avoiding the feeling of having made the wrong choice. Kind of road rage psychology. And anecdotal, YMMV. I think here the soft turbo is a great compromise.

[sputr]

Seems like that from your description the turbo roundabout is only a problem for people who do not know it or know where there are going.

We have both types here. And now that I think about it, the turbo trades a bit more stress on first usage or a lot less every time after that. While the standard 2 or 3 lane is always similarly stresfull.

We do have a partially soft design of turbo roundabouts with phisical deviders and designated places where you can change a lane.