My city has a lot of large roundabouts and a few years ago they made big improvements that reduced the number of incidents and improved traffic flow:
1. They switched from 3 lane traditional to 2 lane spiral roundabouts. There are signs well before you enter the roundabout telling you what lane you need to be in, so you can get into the right lane early. We have a lot of snow in winter, so road markings are not visible.
Example of a sign indicating which lane you need to be in. After this sign, there are two more signs indicating lanes before you get to the roundabout - the next has destination names.
https://maps.app.goo.gl/zJLaFC78i232mUkh6
2. The lanes on the roundabouts have solid white lines which you must not cross. You can only cross lanes to go more towards the center. I'm surprised, but people actually follow this rule.
Example of lanes (and a rare sight of police...)
https://maps.app.goo.gl/HbnkXYkacX3dfq4j6
3. They added speed bumps on the roundabout. This slows down the traffic on the roundabout, giving more chance for vehicles to enter.
https://maps.app.goo.gl/fMKBjocYAFTmpE6ZA