In some of the wine counties that have a lot of tourists, some towns have put in roundabouts. These are not designed to speed traffic; instead they are deliberately designed to slow traffic down. Unfortunately, there is no consistency of visual design.
What can be tolerable to drive in the daytime can become extremely difficult at night, or in bad weather.
One town put a roundabout in as part of a freeway entrance ramp. Driving at dusk I had a difficult time following an unfamiliar twisting road, while accelerating onto the freeway and looking for oncoming traffic in the merging lane!