Roundabouts, when installed according to accepted design principles, offer reductions in injury crashes, traffic delays, fuel consumption and air pollution while increasing intersection capacity and enhancing intersection aesthetics. They also have been successfully used to control traffic speeds in residential neighborhoods and are accepted as one of the safest types of intersection design.

The major differences between traffic circles and roundabouts are:

• Yield at Entry  At roundabouts the entering traffic yields the right-of-way to the circulating traffic. This yield-at-entry rule keeps traffic from locking up and allows free flow movement through the intersection.
  
• Deflection The entry geometry and center island of a roundabout deflect entering traffic to slow the traffic stream and to reinforce the yielding process.
  
• Flare The entry to a roundabout often flares out from one or two lanes to two or three lanes at the yield line to provide increased capacity through the intersection.

There are two basic types of roundabouts  :

• Conventional roundabout A one-way circular roadway around a curbed central island for circulating traffic, usually with flared approaches to allow multiple vehicle entry.
• Mini-roundabout  A one-way circular roadway around a flush or slightly raised central island of up to 15 feet in diameter, usually without flared entries.

Traffic engineers have several reasons why roundabouts are viable traffic control devices to be considered during the investigation of situations which may require some form of traffic control. Among the most often considered reasons are:

1. Safety - Roundabouts have been shown to reduce fatal and injury crashes by as much as 75% in Australia and 86% in Great Britain. The reduction in crashes is attributed to slower speeds through the intersection and to a reduced number of conflict points.

2. Low Maintenance - Roundabouts eliminate maintenance costs associated with traffic signals which amount to $3,000-$5,000 per year per intersection. In addition, the cost of electricity is reduced for a savings of about $1,500-$2,000 per year per intersection.

3. Reduced Delay - By yielding at the entry rather than stopping and waiting for a green light, delay is significantly reduced.

4. Increased Intersection Capacity - Intersections with a high volume of left turns are handled by a roundabout rather than by a multi-phased traffic signal.

5. Reduction of Pollutants - Reduced delay corresponds to a decrease in fuel consumption and a reduction in air and water pollution.

6. Aesthetics - The central island provides an opportunity to provide landscaping. Although landscaping requires maintenance, it also provides a secondary benefit in helping to support adjacent property values.

The correct way to drive a roundabout is simple:

• As you approach a roundabout there will be a YIELD sign and a dashed yield limit line. Slow down, watch for pedestrians and bicyclists, and be prepared to stop if necessary. When you enter, yield to circulating traffic on the left, but do not stop if it is clear.
  
• A conventional roundabout will have ONE WAY signs mounted in the center island. The signs help guide traffic and indicate that you must drive to the right of the center island. Mini-roundabouts may not have one-way signs if the center island is not raised. You must still drive to the right of the domed painted island.
  
• Upon passing the street prior to your exit, turn on your right- turn signal and watch for pedestrians and bicyclists as you exit.
  
• Left turns are completed by traveling around the central island (Figure 3).