Frequently Asked Questions Roundabouts

Frequently Asked Questions

 

Frequently Asked Questions

Roundabouts, rotaries, traffic circles - they're all the same, aren't they?

No.  Other than sharing a circular shape, a modern roundabout operates much differently than other traffic circles, including rotaries.  A modern roundabout requires entering traffic to yield the right-of-way to traffic already in the roundabout.  This keeps the traffic in the roundabout constantly moving and prevents much of the gridlock that plagues rotaries.  Modern roundabouts are also much smaller than rotaries and thus operate at safer, slower speeds.  The design of a modern roundabout allows capacities comparable to signals but with generally a higher degree of safety.

 

Is a modern roundabout like a 4-way stop?

No.  Four way stops require all traffic to stop prior to entering the intersection.  Modern Roundabouts require motorists to YIELD at entry ways. All traffic entering a modern roundabout must follow the golden rule of the modern roundabout - motorists entering a modern roundabout never merge.

 

Are roundabouts appropriate everywhere?

No.  The choice of using a roundabout versus a traffic signal is a case-by-case decision.  Each candidate intersection should be evaluated individually to determine whether a roundabout or a traffic signal is more appropriate.

 

How much traffic can a roundabout handle?

Single-lane roundabouts can typically handle between 20,000 to 26,000 vehicles per day, depending on the number of left-turning vehicles and the distribution of traffic between the major and minor roads.  In general, roundabouts provide greater capacity (accommodate more vehicles) than all way stop control intersections and reduce delays compared to signalized or all-way stop control intersections. The reduced delay of roundabouts is generally attributed to the continuous flow of traffic, all right turn manoeuvres and lower operating speed.

Roundabouts with more than one lane can handle greater traffic volumes.

 

Who has the "Right-of-Way"?

The vehicle in the roundabout has the right of way. The traffic from the connecting roads must yield for the traffic in the roundabout.

 

Why do roundabouts need to be so big?

The size of a roundabout is determined by capacity needs, the size of the largest vehicle, the need to achieve appropriate speeds throughout the roundabout, and other factors.  To handle typical trucks with overall wheelbases of 15 metres or more, a single–lane roundabout needs to be at least 30 metres in diameter and is typically 35 to 50 metres in diameter.

 

Do roundabouts require more space than traditional intersections?

Roundabouts do not necessarily require more space than traditional intersections.  Geometric design details vary from site to site and must take into account traffic volumes, land use, topography, and other factors.  Because they can process traffic more efficiently than traffic signals and stop signs, roundabouts typically require fewer traffic lanes to accommodate the same amount of traffic.  In some cases, roundabouts can require more space than stop signs or traffic signals at the actual intersection to accommodate the central island and circulating lanes, but approaches to roundabouts typically require fewer traffic lanes and less right-of-way than those at traditional intersections.

 

Can large trucks or buses use roundabouts?

Yes.  Modern roundabouts are designed for the largest vehicle reasonably anticipated and, if necessary, are constructed with mountable curbs and truck aprons, which are designed to be driven over by large trucks or buses.  The truck apron generally is composed of a different material texture than the paved surface, such as brick or cobble stones, to discourage routine use by smaller vehicles.

As large vehicles approach the roundabout, they should stay close to the left side of the entry.  As they exit, they should again stay close to the left side of the exit.

 

What should I do when I'm in a roundabout when an emergency vehicle arrives?

Exit the roundabout at the nearest exit and pull over to the right and stop.  Do not stop in the roundabout as you might block the path of a large emergency vehicle.

 

What about snow removal at roundabouts?

A number of communities in snowy areas have installed roundabouts, including Town of The Blue Mountains, Hamilton, Kemptville, and Waterloo in Ontario, and several US cities (Green Bay, Montpelier and Vail).  All have indicated that while there is some initial adjustment in procedures for snowplow crews, roundabouts generally present no major problems for snow removal.

 

Who says that roundabouts are safer?

Several studies have identified that the installation of roundabouts at previous intersections operated by 4-way stop or traffic signals were improved.  Transport Canada is recommending that Canadian jurisdictions consider converting signalized intersections to roundabouts wherever appropriate.  Their findings as well as many others have concluded that countries showing higher reductions of intersection collisions have been implementing roundabouts.  National Collision statistics produced by Transport Canada report 2500 fatal collisions and 145 000 injury collisions each year in Canada.  In 2006, about 28% of road users killed and 40% of those seriously injured was a result of intersection related crashes.

The most recent study was completed by the National Cooperative Highway Research Program (NCHRP Report 572) and identified 26 multi-lane intersections that were converted to multi-lane roundabouts.  The study showed a 67% overall reduction in collisions following implementation of the roundabouts.

 

Why are roundabouts safer?

Roundabouts generally provide a greater level of safety than other types of intersections because of the following characteristics:

Lower speed / Reduced Differential in Speeds: A roundabout’s geometry is designed specifically to direct traffic around the circle at a much slower speed.  Therefore, lower speeds provide more time for all users to detect and correct for their mistakes or if a collision does occur it is less severe due to the lower speeds.

Simplified Decision Making: It’s just Yield Upon Entry.  As a vehicle travels towards a roundabout the geometry and signs will prompt a vehicle to slow down.  As you approach the crosswalk a motorist can detect whether or not to allow for a pedestrian to cross and then they will proceed to the yield line to wait for a gap in the circulating traffic.

Reduced Right Angle and Head On Collisions: The severity of a collision is largely determined by the speed of the impact and the angle of the impact.  The higher the speed, the more severe the collision. The higher the angle of impact, the more severe the collision.  Roundabouts reduce the severity (right angle or head on collisions) that are present in traditional intersections. 

Conflict Points: Roundabouts also significantly reduce the number of conflict points.  A 4-way stop or traffic signal has 32 vehicle to vehicle conflict points and 24 vehicle to pedestrian conflict points for a total of 56, whereas a roundabout has 8 vehicle to vehicle conflict points and 8 vehicle to pedestrian conflict points for a total of 16.  This translates to a reduction of over 70% in the number of potential conflicts if a roundabout is implemented.

What are the common types of collisions at roundabouts?

 

There are two types of collisions that are more common at single lane roundabouts - rear-end collisions and entering collisions.  Rear end collisions occur when a vehicle hits the back of another vehicle, usually at the entrance to the roundabout.  Entering collisions occur when a vehicle entering the roundabout does not yield to a vehicle already in the roundabout.  These collision types are generally only minor "fender benders", as opposed to head on and turning collisions which are often more severe.

 

Aren't traffic signals safer than roundabouts for pedestrians?

It depends on the amount of pedestrians and vehicles.  In many cases a roundabout can offer a safer environment for pedestrians than a traffic signal because the pedestrian crossing at a roundabout is reduced to two simple crossings of one-way traffic moving at slow speeds.  A pedestrian crossing at a traffic signal still needs to contend with vehicles turning right or left on green, vehicles turning right on red and vehicles running the red light.  The latter of these potential conflicts occur at high speeds and often result in injuries or fatalities to pedestrians.

Many studies have shown a pedestrian’s risk of being involved in a severe collision is lower at roundabouts, due to the slower vehicle speeds.  Also, as previously stated, the number of conflict points for a pedestrian is lower at a roundabout then at other intersections, which lowers the frequency of collisions. A Dutch study of 181 intersections converted to roundabouts found a reduction in all pedestrian crashes of 73%.

 

How about cycling through a roundabout?

A cyclist has a number of options at a roundabout and the choice will depend on the degree of comfort riding in traffic. The speed of cars through a roundabout is close to the speed you ride your bicycle. You can choose to either circulate as a vehicle or use the sidewalk around the roundabout. When circulating as a vehicle, be sure to ride near the middle of the lane so that drivers can see you and will not attempt to pass you. Cars should be travelling at speeds similar to your speed within the circular roadway portion of the roundabout.

 

Will modern roundabouts be more difficult than traffic signals for senior drivers?

Roundabouts eliminate many of the driving scenarios that can be challenging for older drivers. Relative to other age groups, senior drivers are over-involved in crashes occurring at intersections.  In 2008, 37% of drivers 70 and older in fatal crashes were involved in multiple-vehicle intersection crashes, compared with 22% among drivers younger than 70.  Older drivers' intersection crashes often are due to their failure to yield the right-of-way.  Particular problems for older drivers at traditional intersections include left turns and entering busy roads from cross streets.  Roundabouts eliminate these situations entirely.  A 2007 study in six communities where roundabouts replaced traditional intersections found that about two-thirds of drivers 65 and older supported the roundabouts.15

Two comprehensive studies of modern roundabouts in the US reported that any crashes occurring after replacing traffic signals with modern roundabouts did not reflect an increase in driver age. Although not conclusive, these reports suggest that modern roundabouts do not pose a problem for older drivers. 

 

Are modern roundabouts more costly to construct?

The cost of modern roundabouts vs traditional intersections can vary.  Demographics, geography and environmental elements all come into play when engineers and planners begin to consider how to move traffic through from one street to another.  Sometimes the cost to acquire the lands is higher than the cost of traffic signals whereas other times it is not a factor.  When safety factors go up, the cost to society emotionally and physically goes down. Once accident and users costs are calculated, the installation of traffic signals would be much more costly over time than the construction of a roundabout. The safety and environmental issues related to traffic signal intersections are also greatly improved with a roundabout.

 

Are modern roundabouts more costly to maintain?

Modern roundabouts do not require traffic light electricity, but the maintenance of landscaping is a cost.

 

Why are roundabouts considered more aesthetically pleasing?

There is typically more green space available at roundabouts then at signalized intersections. The center island at a roundabout can be utilized as gateways to communities. The center island can be landscaped using such treatments as trees, shrubs, flower beds, public art, etc. As pedestrians are not encouraged to utilize the center island for an activity the landscaped features should not encourage pedestrians to explore the center island. Roundabouts can also provide opportunities for traffic calming and speed transition within neighborhoods.

 

Are roundabouts better for the environment?

Vehicles operating in a roundabout result in lower environmental impacts, by keeping traffic moving at a more consistent lower speed and reducing idling.  The shorter delays and “rolling” approach to roundabouts generally reduce fuel and energy consumption, greenhouse gas emissions, the carbon footprint, as well as a reduction in noise to the surrounding community.  The longer delays and the start and stop approach to signalized intersections will generally have a more demanding impact on the environment.

 

Why haven't more roundabouts been built?

Despite the safety and other benefits of roundabouts, as well as the high levels of public acceptance once they are built, some areas have been slow to build roundabouts, and some are even opposed to building them.  The main obstacle is the negative perception held by some drivers and elected officials.  Transportation agencies also have long been accustomed to installing traffic signals, and it can take time for deeply rooted design practices to change.

What do the signs at a roundabout mean?

Roundabout Ahead Sign. Time to slow down.

Keep to the Right

Yield to all traffic in the roundabout including pedestrians at the crosswalk.  Remember that “yield” means you may have to stop.  Traffic in the roundabout always has the right of way.

This sign is located on the center island reminding the driver to travel the roundabout in a one way counter clockwise direction

Pedestrian Crossing