What is a Roundabout?

A roundabout is a circular intersection where traffic flows around a center island.

Advantages of roundabouts:

  • Roundabouts are safe.
  • Since vehicles entering the roundabout are required to yield to traffic in the circle, more vehicles can move through the intersection with less delay.
  • Roundabouts are less costly than intersection widening.
  • The unique one-way design of roundabouts accommodates the turning radius of large vehicles, like semi-trucks and buses.
Characteristics of Roundabouts
Control at Entry Yield sign for entering vehicles
Operational Characteristics Vehicles in the roundabout will have a priority over the entering vehicle.
Deflection Use deflection to control the low speed operation through roundabout.
Parking No parking is allowed on the circulating roadway.
Pedestrian Crossing No pedestrian activities take place on the central island.
Turning Movement All vehicles circulate around the central island.
Splitter Island Required.

How Roundabouts Work

Video courtesy of the Insurance Institute for Highway Safety 
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History of the Modern Roundabout

Westview RoundaboutThe roundabout concept was first invented in the early 1900’s and deployed throughout Europe and America. A modern roundabout has three major characteristics compared to its predecessors, traffic circles and rotaries:

  • The roundabout gives vehicles in the circular travel way the right-of-way.
  • Roundabouts are small, generally from 70 to 160 feet in diameter compared to 300 to 400 feet and more for traffic circles and rotaries.
  • Roundabouts have a raised entry "splitter" island that slows down or constrains speed just before entry, duplicating the curvature the driver will experience within the roundabout itself.

During the 1950’s there was a loss of confidence in roundabouts, due mainly to the problem of traffic locking and the increasing number of accidents. Many were replaced by traffic signals.

In 1966, the off-side priority rule (an entering vehicle gives way to vehicles in the roundabout) and the yield at entry operation enhanced roundabout capacity and safety performance. The success of this modern roundabout inspired renewed interest in roundabouts worldwide.

The modern roundabout finally arrived in the United States in 1990 in Summerlin, a major Las Vegas residential subdivision. When the first roundabout freeway interchange in the nation was built in 1995 (at the I-70 interchange in Vail, Colorado), roundabouts then numbered about a dozen nationally. Roundabouts have since been constructed in every state including Alaska and Hawaii.

As of January 2006, the number of modern roundabouts in the USA had leaped to around 1,000. Roundabout proponents anticipate that roundabouts will be built in the United States by the thousands in the near future.

Sources: RoundaboutsUSAOregon Department of Transportation
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Features of a Roundabout

Roundabout Features
Image Source: Federal Highway Administration

The central island is the raised area in the center of a roundabout around which traffic circulates.

A splitter island is a raised or painted area on an approach used to separate entering from exiting traffic, deflect and slow entering traffic, and provide storage space for pedestrians crossing the road in two stages.

The circulatory roadway is the curved path used by vehicles to travel in a counterclockwise fashion around the central island.

If required on smaller roundabouts to accommodate the wheel tracking of large vehicles, an apron is the mountable portion of the central island adjacent to the circulatory roadway.

A yield line is a pavement marking used to mark the point of entry from an approach into the circulatory roadway and is generally marked along the inscribed circle. Entering vehicles must yield to any circulating traffic coming from the left before crossing this line into the circulatory roadway.

Accessible pedestrian crossings should be provided at all roundabouts. The crossing location is set back from the yield line, and the splitter island is cut to allow pedestrians, wheelchairs, strollers, and bicycles to pass through.

Bicycle treatments at roundabouts provide bicyclists the option of traveling through the roundabout either as a vehicle or as a pedestrian, depending on the bicyclist’s level of comfort.

Landscaping buffers are provided at most roundabouts to separate vehicular and pedestrian traffic and to encourage pedestrians to cross only at the designated crossing locations. Landscaping buffers can also significantly improve the aesthetics of the intersection.

Source: Federal Highway Administration 
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How to Use Roundabouts - Drivers

Runnymeade RoundaboutApproaching the roundabout

  • Decide as early as possible which exit you need to take and get into the correct lane.
  • Reduce your speed.
  • Bicyclists are vehicles and need to share the lane at intersections. Therefore, allow bicycles to enter the roadway from any bicycle lane.
  • The law gives pedestrians the right-of-way in a crosswalk. Yield to pedestrians waiting to cross or crossing on the approach.
  • Watch out for and be particularly considerate of people with disabilities, children, and elderly pedestrians.
  • Always keep to the right of the splitter island.

Entering the roundabout

  • Upon reaching the roundabout yield line, yield to traffic circulating from the left.
  • Do not enter the roundabout beside a vehicle already circulating within the roundabout, as a vehicle near the central island may be exiting at the next exit.
  • Watch out for traffic already on the roundabout, especially cyclists and motorcyclists.
  • Do not enter a roundabout when an emergency vehicle is approaching on another leg; allow queues to clear in front of the emergency vehicle.

Within the roundabout

  • Do not stop except to avoid a collision; you have the right-of-way over entering traffic.
  • Always keep to the right of the central island and travel in a counterclockwise direction.
  • Do not overtake adjacent vehicles who are slightly ahead of yours as they may wish to exit next.
  • Watch out for traffic crossing in front of you on the roundabout, especially vehicles intending to leave by the next exit.
  • Do not change lanes within the roundabout except to exit.
  • When an emergency vehicle is approaching, proceed past the splitter island of your exit before pulling over.

Turning at roundabouts

Turning Right or Exiting at the First Exit Around the Roundabout

  • Turn on your right-turn signal on the approach.
  • If there are multiple approach lanes, use only the right-hand lane.
  • Keep to the outside of the circulatory roadway within the roundabout and continue to use your right-turn signal through your exit.
  • When there are multiple exit lanes use the right-hand lane.

Going Straight Ahead (Exiting Halfway Around the Roundabout)

Going Straight Ahead
Image Source: Federal Highway Administration,
from The Highway Code (UK) (9), converted to right-hand drive
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  • Do not use any turn signals on approach.
  • If there are two approach lanes, you may use either the left– or right-hand approach lanes.
  • When on the circulatory roadway, turn on your right-turn signal once you have passed the exit before the one you want and continue to use your right turn signal through your exit.
  • Maintain your inside (left) or outside (right) track throughout the roundabout if the circulatory roadway is wide. This means that if you entered using the inner (left) lane, circulate using the inside track of the circulatory roadway and exit from here by crossing the outside track. Likewise, if you entered using the outer (right) lane, circulate using the outside track of the circulatory roadway and exit directly from here. Do not change lanes within the roundabout except when crossing the outer circulatory track in the act of exiting.
  • When exiting the circulatory roadway from the inside track, watch out on the outside track for leading or adjacent vehicles that continue to circulate around the roundabout.
  • When exiting the circulatory roadway from the outside track, yield to leading or adjacent vehicles that are exiting into the same lane.

Turning Left or Making a U-turn

Turning Left or U-Turn
Image Source: Federal Highway Administration,
from The Highway Code (UK) (9), converted to right-hand drive
(This link will open in a new window)

  • Turn on your left turn signal.
  • If there are multiple approach lanes, use only the left-hand lane.
  • Keep to the inner (left) side of the circulatory roadway (nearest the central island).
  • Continue to use your left-turn signal until you have passed the exit before the one you want, and then use your right-turn signal through your exit.
  • When exiting from a multilane roundabout from the inside part of the circulatory roadway, use only the inner lane on the exit (the lane nearest the splitter island). Watch out on the outside part of the circulatory roadway for leading or adjacent vehicles that continue to circulate around the roundabout.

When in Doubt About Lane Choice

  • If you intend to exit the roundabout less than halfway around it, use the right lane.
  • If you intend to exit the roundabout more than halfway around it, use the left lane.

Exiting the roundabout

  • Maintain a slow speed.
  • Always indicate your exit using your right-turn signal.
  • For multilane roundabouts, watch for vehicles to your right, including bicycles that may cross your path while exiting.
  • Watch for and yield to pedestrians waiting to cross, or crossing the exit leg.
  • Watch out for and be particularly considerate of people with disabilities, children, and elderly pedestrians.
  • Do not accelerate until you are beyond the pedestrian crossing point on the exit.

Motorcyclists and bicyclists

  • Watch out for motorcyclists and bicyclists. Give them plenty of room and show due consideration.
  • Bicyclists may enter the approach roadway from a bicycle lane. Bicyclists will often keep to the right on the roundabout; they may also indicate left to show they are continuing around the roundabout.
  • It is best to treat bicyclists as other vehicles and not pass them while on the circulatory roadway.

Large vehicles

  • When car drivers approach a roundabout, do not overtake large vehicles. Large vehicles (for example, trucks and buses) may have to swing wide on the approach or within the roundabout. Watch for their turn signals and give them plenty of room, especially since they may obscure other conflicting users.
  • Drivers of large vehicles may need to use the full width of the roadway, including mountable aprons if provided. They should be careful of all other users of the roundabouts and satisfy themselves that other users are aware of them and will yield to them.

How to Use Roundabouts - Cyclists

Bicyclists should enter roundabouts just as they enter a stop sign or signal controlled intersection without auxiliary lanes. On the approach to the entry, a bicyclist should claim the lane. Right-turning cyclists should keep to the right side of the entry lane; others should be near the center of the lane.

Cyclists have three options upon approaching a roundabout:

  • Travel on the circulatory roadway of the roundabout like motorists. When using a double-lane roundabout as a vehicle, obey all rules of the road for vehicles using roundabouts. However, you may feel safer approaching in the right-hand lane and keeping to the right in the roundabout. If you do keep to the right, take extra care when crossing exits and signal left to show you are not leaving.
  • If you are unsure about using the roundabout, dismount and exit the approach lane before the splitter island on the approach, and move to the sidewalk. Once on the sidewalk, walk your bicycle like a pedestrian.
  • Some roundabouts may have a ramp that leads to a widened sidewalk or a shared bicycle-pedestrian path that runs around the perimeter of the roundabout. If a ramp access is provided prior to the pedestrian crossing, you may choose to ramp up to curb level and traverse the sidewalk or path while acting courteously to pedestrians.

How to Use Roundabouts - Pedestrians

Pedestrians have the right-of-way within crosswalks at a roundabout. However, pedestrians must not suddenly leave a curb or other safe waiting place and walk into the path of a vehicle if it is so close that it is an immediate hazard.

  • Do not cross the circulatory roadway to the central island. Walk around the perimeter of the roundabout.
  • Use the crosswalks on the legs of the roundabout. If there is no crosswalk marked on a leg of the roundabout, cross the leg about one vehicle-length away from the circulatory roadway of the roundabout. Locate the wheelchair ramps in the curbs. This opening is for pedestrians to wait before crossing the next roadway.
  • Roundabouts are typically designed to enable pedestrians to cross one direction of traffic at a time. Look and listen for approaching traffic. Choose a safe time to cross from the curb ramp to the median opening. If a vehicle slows for you to cross at a two-lane roundabout, be sure that conflicting vehicles in adjacent lanes have done likewise before accepting the crossing opportunity.
  • Most roundabouts provide a raised median island halfway across the roadway; wait in the opening provided and choose a safe time to cross traffic approaching from the other direction.

Source: Federal Highway Administration 
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