Both roundabouts and traffic signals are used to control major intersections with relatively high volumes and speeds. At roundabouts a deflection angle approaching the intersection directs drivers to merge with traffic. Intersections with traffic signals have traffic entering at 90 degree angles. With roundabouts, direct left-turn and u-turn movements are eliminated by making the driver rotate around the circle to the desired destination leg of the intersection. With traffic signals, left-turns and u-turns cross against opposing traffic with or without their exclusive phases.

Several factors contribute to increasing delay and collision rates at traffic signals compared to roundabouts:

• The higher the volume using the intersection, the higher the number of signal phases needed, regardless of the number of lanes available. For each phase a minimum green, yellow and all-red time must be provided.

• For intersections with no exclusive left-turn lanes, through traffic may lose a significant portion of its green time impeded by one left-turner.

• Signals require costly year-round maintenance and energy.

• Collisions at signalized intersections are more likely, because of the added conflicts related to left-turns and u-turns. No direct left-turns or u-turns exist at roundabouts.

• Roundabouts have fewer conflict points - eight conflict points for a four-way roundabout, compared to 32 for a signalized intersection.

• Collisions at signalized intersections are usually more severe, since they occur at high speeds and often either head-on or at 90°. Accidents at roundabouts are generally low-speed rear-end or merge crashes.