As a systems guy I love roundabouts. They make it so much easier to get across intersections and they completely eliminate the variable cost of left hand (right hand if you're British) turns. That is because traversing them and exiting simply a linear function of traffic and not based on whether or not there is a special light for cross traffic turns which may or may not be timed appropriately. Thus it is always the "fastest" way to get from point A to point B by travelling along the highest flow routes.
That differs in the US where travelling a slower, but less controlled side street can be faster than using boulevards with left turn lights.
That differs in the US where travelling a slower, but less controlled side street can be faster than using boulevards with left turn lights.