Roundabouts vs. Traffic Circles
A roundabout is a circular intersection similar to the traffic circle previously used in this country. The major differences between a traffic circle and a roundabout are:
- Yield at Entry
- At roundabouts the entering traffic yields the right-of-way to the circulating traffic. This yield-at-entry rule prevents traffic from locking-up and allows free flow movement.
- Deflection
- The entry and center island of a roundabout deflects entering traffic to slow traffic and 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.
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Types of Roundabouts
There are two basic types of roundabouts (See Figure 1):
- 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 13 feet in diameter, usually without flared entries.
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Why Use a Roundabout?
- Safety--Roundabouts have been shown to reduce fatal and injury accidents as much as 76% in the USA, 75% in Australia and 86% in Great Britain. The reduction in accidents is attributed to slower speeds and reduced number of conflict points (see Figure 2).
- Pedestrian Safety--All research suggests that modern roundabouts are safer than signalized intersections for pedestrians. This safety advantage has been attributed to the slower traffic speed at roundabouts and the division of the pedestrian crossing into two stages, from the near-side wheelchair ramp out to the splitter island, and then from the splitter island to the far-side wheelchair ramp. In each stage the pedestrian has to look in only one direction to cross a one-way traffic stream. Pedestrian refuges are provided in the areas within the splitter islands.
- Low Maintenance--Eliminates maintenance costs associated with traffic signals which amount to approximately \\$3,500 per year per intersection. In addition, electricity costs are reduced with a savings of approximately $1,500 per year per intersection.
- Reduced Delay--By yielding at the entry rather than stopping and waiting for a green light, delay is significantly reduced.
- Capacity--Intersections with a high volume of left turns are better handled by a roundabout than a multi-phased traffic signal.
- Aesthetics--A reduction in delay corresponds to a decrease in fuel consumption and air pollution. In addition, the central island provides an opportunity to provide landscaping.
Figure 2: Conflict Points on a Regular 4-way Intersection Compared to a Modern Roundabout Intersection
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How to Drive a Roundabout
- As you approach a roundabout there will be a YIELD sign and 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 the way is clear.
- A conventional roundabout will have ONE-WAY signs mounted in the center island. They help guide traffic and indicate that you must drive to the right of the center 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 (see map below).
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