Roundabouts are unfair. They don't balance traffic loads symmetrically.
Here is what I have observed at one near my house: as you approach the yield line, you can't enter the circle if someone has just entered it on your left. So, if you have lots of cars approaching northbound, and lots of cars approaching westbound, the northbound cars will be on the left of the westbound ones, and will block their entry. You end up with a huge queue on the westbound lane.
This is exactly what happens every day at the evening rush hour (and of course the southbounders block the eastbounders in the morning).
A traffic light would be much better, because its red/green intervals can be tuned to observed traffic tendencies for the time of day.
Here is what I have observed at one near my house: as you approach the yield line, you can't enter the circle if someone has just entered it on your left. So, if you have lots of cars approaching northbound, and lots of cars approaching westbound, the northbound cars will be on the left of the westbound ones, and will block their entry. You end up with a huge queue on the westbound lane.
This is exactly what happens every day at the evening rush hour (and of course the southbounders block the eastbounders in the morning).
A traffic light would be much better, because its red/green intervals can be tuned to observed traffic tendencies for the time of day.