I grew up near Skelmersdale which is a ‘new town’ built in the 60’s without traffic lights, all roundabouts. Traffic is segregated from pedestrians using underpasses and footpaths don’t follow roads generally.
Some aspects of it work well. It’s pleasing and efficient not to have to stop much when you’re getting places.
The underpasses have become magnets for anti social behaviour though.
The mistake is that the cars should use the subways/underpasses since they are inherently antisocial already. The antisocial types can then all hang out together.
How does that work for bicycles? As a cyclist most roundabouts are OK but busy multi-lane ones can be pretty terrifying if you need to turn against the traffic flow (i.e., taking the 3rd exit, right for me, but left if in the US or any country you drive/ride on the right side of the road). I've yet to see a decent solution to that.
The best answer is a completely separate bikeway that crosses outside the roundabout, or passes over/under the road.
But, if that's not possible, the bike is either acting like another car (in the roundabout) or a pedestrian (crossing several entry/exit points). Less than ideal, but still better than getting t-boned at >30kph as happens at 4-way stops in the US.
Here's an example, but it relies on drivers yeilding to cyclists (they're supposed to but usually don't in the US, regardless of intersection and signage).
https://www.youtube.com/watch?v=wEXD0guLQY0
Yeah even that Netherlands one (which is only possible if there's a lot of space available) relies way too much on drivers actually bothering to look out for bikes. I'd rather have traffic lights to be honest.
