The city of Forest Lake, Minnesota is going to deploy a slew of roundabouts to control traffic, replacing traffic lights. This article describes the plan: St. Paul Pioneer Press | 09/09/2006 | Roundabout plan may get a trial spin
In most studies of the issue, roundabouts improve on safety and reduce delay compared with traffic signals. They have the advantage of minimizing conflict points at intersections, and help keep drivers moving, while slowing them down and making them more alert.
This wikipedia article describes roundabouts in more depth.
Unfortunately, traffic circles have given roundabouts a bad name, and becaues they are not so complicated, they are often not even taught in Traffic Engineering classes, so they are not given due placement in the traffic engineers toolbox.

In an op-ed published in today’s Washington Post: Peace On the Roads, Oscar Arias, President of Costa Rica and winner of the Nobel Peace Prize decries the lives lost on roads, particularly in the developing world. Clearly this is an under-appreciated problem, because it does not have the flash of a plane crash or terrorism, but we lose more people in the US each month to traffic crashes than we do each year (or decade) to terrorism. The toll in the developing world is much worse on a per-vehicle-km traveled basis, because roads are worse, drivers are worse (have less driver education), enforcement is worse, and vehicles are worse. While zero deaths is a long way off, 1.2 million per year can certainly be reduced.