Modern Roundabouts ~ FAQ

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A look at modern roundabout use in the USA in the last ten years indicates motorists are initially hesitant about their advantages, safety and usefulness.

In many communities, the initial hesitation gives way to support when the advantages demonstrated by this new form of traffic control management become evident . . .

	90 percent reduction in fatal crashes
	75 percent reduction in injury crashes
	30-40 percent reduction in pedestrian crashes
	10 percent reduction in bicycle crashes
	30-50 percent increase in traffic capacity thereby enhancing traffic flow

The ADOT Modern Roundabout Video
Request a DVD	English	Spanish
Introduction 2:25 minutes
Full Length 8:10 minutes
	Video Script (file size: 73KB)	Video Script (file size: 49KB)

MODERN ROUNDABOUTS ARE ALSO ASSOCIATED WITH OTHER BENEFITS

	Reduction in fuel use
	Reduction in pollution
	No signal equipment to install and repair
	Reduction in noise due to fewer stops/starts (quieter neighborhoods)

The safety features of the modern roundabout overcome initial skepticism and contribute to their growing popularity.

Studies reporting dramatic reductions in fatal crashes, injury crashes and pedestrian crashes attributed to modern roundabouts are very impressive.

Arizona and the City of Phoenix have the nation’s worse scores for fatalities resulting from red light runners at traditional intersections! Modern roundabouts -- a one way circular intersection without signals -- are designed to reduce this grim statistic by slowing down and calming traffic.

Like any new development, modern roundabouts inspire questions. Some of the most common inquiries are discussed in the following sections. And, of course, if your questions are not answered below, simply contact ADOT. We welcome the opportunity to answer you directly.

“ARE THE BENEFITS OF MODERN ROUNDABOUTS BASED ON SEVERAL STUDIES OR ONLY ONE?”

The fact that the modern roundabout is the safest form of intersection control available has been verified worldwide, and in the USA by several recent studies of intersection safety.

Probably the most comprehensive US study to date, the Insurance Institute for Highway Safety completed an in depth study of 24 intersections -- in a mix of urban, suburban and rural environments, which had been converted from stop control and signals to modern roundabouts. (Crash Reduction Following Installation of Roundabouts in the United States, Insurance Institute for Highway Safety, Arlington, VA: Status Report, May, 2000.) This study reported reductions of 39 percent for all crash severities combined, 76 percent of all injury crashes and an approximate 90 percent in fatal and incapacity injury crashes.

“WHAT’S THE DIFFERENCE BETWEEN AN "OLD" TRAFFIC CIRCLE AND A MODERN ROUNDABOUT?”

Modern roundabouts are quite different from those big, old, high speed traffic circles built years ago in Washington, DC and other eastern cities as well as Paris and London. Designed for high speed entry and multi-lane weaving, these traffic circles generally suffered high crash rates and operational problems causing many to fall out of favor in the USA during the 1950s and 1960s.

Though roundabouts had been used in Great Britain since the beginning of the 20th century, there were problems such as stalled traffic. The engineers decided to make a good idea even better. And by 1966, British engineers came up with the yield at entry rule. This ended the “locking” problem, improved capacity, and reduced crashes.

In the mid-70s, another variable was added -- the curved vehicle path or deflection. This helped decrease speed while “speeding” circulating time.

Many traffic circles require circulating vehicles to grant the right of way to entering vehicles.

Traffic Circles can be very large or very small. The sizes of traffic circles are determined by land availability and/or road distance needed for high speed weaving movements. They can operate at higher speeds and often require motorists to move from one lane to another.

The term Modern Roundabout became popular by 1984 because of improvements such as yielding to as opposed to merging with circulating traffic, deflection at entry, and low design speed.

In addition to slower speeds and curved entries, advantages of Modern Roundabouts also include the fact they are designed using rigorous standards based on specific turning volumes.

“IS A MODERN ROUNDABOUT LIKE A 4 WAY STOP?”

No a modern roundabout is not a 4 way stop. Both intersections are what the engineering community calls a “method of moving traffic”. 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.

All motorists approaching a roundabout must slow down and yield. Other differences between roundabouts and 4 way stop intersections include:

	Four way stops yield to the right while roundabouts yield to the left (similar to a right turn on red.) This pattern is dictated by the fact that circulating traffic in a roundabout comes from the left.
	Traffic in a Modern Roundabout circulates counter clockwise.
	Motorists coming from different directions get a turn in order at a four way stop. This is not the case with roundabouts where each driver chooses a safe gap to enter rather than taking a “turn”.

There is one outstanding similarity between modern roundabouts and 4 way stop intersections - neither one has traffic signals.

“HOW DO I ENTER A MODERN ROUNDABOUT WHEN TRAFFIC IS CONGESTED?”

First of all, know where you are going. Do you want to take a right hand turn? Go straight ahead? Take a left hand turn? Or make a U turn? However, follow the pavement markings and signage.

Secondly, slow down! You should be approaching a modern roundabout no more than 25 mph.
Most importantly, you do not merge. Always yield to traffic in circulation when entering a modern roundabout.

Do not attempt to cut in front! Wait for a safe gap in the traffic . . . remember those drivers already in the roundabout have the right of way.

The Users Guide offers more details and the following animations will "walk you through" several modern roundabout scenarios. You will experience how easy it is to enter and exit a modern roundabout and what will result with improper use.

	Choosing the proper lane.
	Yield to pedestrians.
	What to do when encountering emergency vehicles.
	Using the truck apron for large vehicles.
	Improper lane change results in crash.
	Wrong assumption leads to crash.


“ARE THE CIRCULATORY ROADWAYS OF A MULTI-LANE MODERN ROUNDABOUT STRIPED?”
	Yes, there are many applications for striping and lane marking. For the driver’s ease of entry, spiral striping is used when a modern roundabout has one or more entries that have dual left turns. This visual guide enables a vehicle that enters the roundabout prior to the entry with the dual lefts to be "spiraled" from the inside lane to the outside lane without having to cross over lane lines. Spiral striping prevents a vehicle in the interior lane from being trapped by the dual left turning vehicle in the outside lane. Spiral striping also prevents vehicles from making unsafe exits from the wrong lane. This diagram is also available in a printable PDF version. You can also check out the Users Guide.

“WILL MODERN ROUNDABOUTS SLOW TRAFFIC DOWN? TRAFFIC SIGNALS HANDLE HIGHER VOLUMES, RIGHT?”

In most situations, a modern roundabout can handler higher traffic volumes with less delay than traffic signals. Even with drivers slowing down to 15-25 mph! Motorists are not stopping for traffic lights.

A two lane roundabout will handle the same capacity as other major intersections in the Valley and a three lane roundabout handles up to 6,000 vehicles an hour.

“WILL MODERN ROUNDABOUTS BE MORE DIFFICULT THAN TRAFFIC SIGNALS FOR SENIOR DRIVERS?”

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 ROUNDABOUTS SAFE FOR PEDESTRIANS AND BICYCLISTS?”

While it depends on the number of pedestrians and vehicles, in many instances, a modern roundabout can be safer for pedestrians than a traffic signal. This is due to the fact that a pedestrian crossing is reduced to two simple crossings of one way traffic proceeding at relatively slow speeds.

Pedestrian safety is enhanced by the presence of a Pedestrian Crosswalk sign placed right before a vehicle enters a modern roundabout. Even with this precaution, it is recommended that pedestrians use caution and always use the designated crosswalk.

Auto-pedestrian crash rates are usually lower at modern roundabouts than traffic signals Also pedestrian injuries that do occur tend to be less serious thanks to the relatively low speeds demanded by modern roundabouts.

Properly designed modern roundabouts safely accommodate bicycles. Because vehicles are traveling at 15-25 mph -- comparable to bicycle speeds -- bicyclists can negotiate this traffic mode like a car.

For more information regarding pedestrian and bicycle use of modern roundabouts, consult the subsection in the Users Guide.

“WHAT ABOUT MOTORCYCLES AND MOTOR BIKES?”

These vehicles are subject to the same rules as cars, trucks, etc. Motorcycle and motor bike riders should consult the Users Guide, with special attention being paid to the subsection entitled 'How to Drive a Modern Roundabout'.

“WHAT DO I DO IF AN EMERGENCY VEHICLE ARRIVES WHEN I’M IN A MODERN ROUNDABOUT?”

Modern roundabouts are designed to accommodate emergency and other large vehicles. If the roadway is wide enough, pull over as far to the right as possible and let the vehicle pass. Whenever possible, completely clear the modern roundabout and pull off to the side.

Any time lost negotiating the modern roundabout -- where speeds are 15-25 mph will only be a few seconds.

For more information, check out the Users Guide.

“WHAT’S THE PRICE TAG? ARE MODERN ROUNDABOUTS MORE COSTLY?”

The price tag of modern roundabouts versus traditional more familiar methods of moving traffic through 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. The variables in the decision making process, community involvement and growth patterns influence how transportation professionals and city and state planners make decisions about how to move traffic.

Sometimes the price tag for right of way acquisition is higher than the price tag of traffic signal construction and sometimes it is not a factor.

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

The construction of modern roundabouts is not a panacea for all new traffic intersections, like other ways to move traffic through intersections it is a tool in a tool box increasing numbers of Departments of Transportation in the USA are beginning to take a serious look at.

The Insurance Institute for Highway Safety statistics show there are fewer serious accidents in Modern Roundabouts. There are fewer and fatal crashes in modern roundabouts.

When safety factors go up, the cost to society emotionally and physically goes down.

“WHEN IS A MODERN ROUNDABOUT COMING TO MY NEIGHBORHOOD?”

Modern roundabouts are not appropriate for use everywhere but if the community leaders in your area are considering a Modern roundabout ADOT will respond appropriately.

If you have questions about modern roundabouts near you call your local ADOT District, or take a look at the Arizona Modern Roundabouts page of to learn about which ones are currently under construction as well as sites being considered for future construction.