Modern Roundabouts ~ History

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Designed to calm traffic, the modern roundabout is a raised, one way circular intersection that promotes safe and efficient vehicle movement.

It incorporates a yielding right of way design to reduce traffic accidents, delays and speeds.

Modern roundabouts in the United States require vehicles to travel counterclockwise, with entering traffic yielding the right of way to circulating traffic.

You never merge: all motorists approaching a roundabout must yield. Drivers entering a roundabout must slow down to approximately 15-25 mph, avoid potential conflicts with vehicles already in the circle, and be prepared to stop for pedestrians and bicyclists.

Once in the roundabout, drivers proceed to the appropriate exit, guided by traffic signs and pavement markings.

Modern roundabouts were developed in the United Kingdom in the 1960s, and have been widely used throughout Europe and Australia as a form of intersection control during the past four decades.

The first modern roundabouts in the United States were constructed in Nevada in 1990. More than 23 states, including California and New York, have active programs to construct roundabouts. More than a thousand modern roundabouts have been built in the USA since 1990!

Did you know . . . modern roundabouts actually “began” more than a century ago?

CIRCULAR TRAFFIC CONTROL METHODS OF THE PAST

The concept of a circular intersection dates back to 1903, when a “gyratory” operation for traffic control was adopted by the French at Place de l’Etoile (now Place Charles de Gaulle.)

During the early half of the 20th century, numerous gyratory systems (traffic circles or rotaries) were built throughout the United States.

Unfortunately, both the design and traffic conditions at that time led to severe problems with gyratory systems.

GENERAL PROBLEMS WITH GYRATORY SYSTEMS
The lack of support for modern roundabouts on the part of a few in the United States -- as contrasted with their overwhelming popularity in Europe and Australia -- can usually be traced back to the problems with gyratory systems (traffic circles or rotaries) initially encountered by motorists.
During the time when these systems were first installed, local ordinances were not enforceable and uniform rules of the road were still being developed. Consistent, right of way rules did not exist throughout the country; practices differed throughout the United States. For instance, some states opted for a “first in” provision. Strange as it may seem nowadays, the yield rule was not practiced until the early 1950s! Of course, right of way considerations were not too important early on when traffic was fairly sparse.
However, as communities grow, traffic speeds and traffic management change. And traffic control devices reflect these changes. (Remember when cars didn’t have traffic signals and motorists had to use their arms to signal their turning intentions?) The Manual on Uniform Traffic Control Devices, created by the United States Department of Transportation (USDOT), underwent eight editions since first being issued in 1927. (The need to continually update these editions is indicative of the many changes that occurred since the original publication.)


TRAFFIC CIRCLES
	Originally designed to lower speeds on residential streets, traffic circles are circular intersections. They tend to be large in diameter, have high circulating speeds, and can require some merging and weaving between lanes to exit. Unlike modern roundabouts, traffic circles give entering traffic the right of way, requiring circulating traffic to yield.
Traffic circles can involve stop signs or signals, and be very large or very small. In addition, they often require motorists to move from one lane to another and operated at higher speeds.

Modern roundabouts have a smaller diameter than most traffic circles, resulting in slower speeds typically 15-25 mph.

The signs as well as the flared and sometimes striped approaches (which direct and guide the motorist), entry angles, slower speeds, and the mandatory yield to circulating traffic at the point of entry make modern roundabouts easy to see, easy to enter and easy to use.

Furthermore, modern roundabouts are designed using rigorous standards based on specific turning volumes.

On the other hand, traffic circles are typically sized according to land availability and/or road distance needed for high speed weaving movements.

ROTARIES

Rotary is the term used in the Eastern United States for the older style circular intersections.

Like traffic circles and unlike modern roundabouts, rotaries give entering traffic the right of way, requiring circulating traffic to yield.

Two other major differences between rotaries and modern roundabouts include:

As opposed to the small diameters of modern roundabouts, rotaries typically have diameters greater than 300 feet.
This feature allows for higher circulatory speeds, which results in different speeds between circulating and entering traffic.


GYRATORY SYSTEMS FALL OUT OF FAVOR
As traffic volumes increased, an increased number of traffic circles tended to lock up. Traffic would literally come to a halt, until the police intervened. After some severe safety and operational mishaps (due in large part to large circles and high speeds), gyratory systems fell out of favor with both motorists and engineers in the United States by the 1950s.


THE MODERN ROUNDABOUT EMERGES . . .
	While the Americans gave up on gyratory systems for a while, the British continued to refine roundabout designs. (The word “roundabout” was officially adopted by the British to replace the term “gyratory” in 1926.) Adopted by the British in 1960, the mandatory yield at entry rule was a very dramatic and important change in the success and use of modern roundabouts.
While the United States had dismissed the modern roundabout as being not very functional, British engineers disagreed. They had discovered that modern roundabouts worked very efficiently if motorists entering the roundabout yielded to circulating traffic.

MOTORISTS CIRCULATING IN THE MODERN ROUNDABOUT ALWAYS HAVE THE RIGHT OF WAY

The traditional “yield to the right (entering)” rule of traffic circles and rotaries vis à vis the “yield to the left (circulating)” rule of modern roundabouts is a very basic and important difference between the two types of intersection control.

Remember this golden rule: You never merge; all motorists approaching a roundabout must yield.

When the golden rule of yielding at entry to circulating traffic is understood and followed, modern roundabouts work very well.

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)

Realize that the motorists circulating in the circle, driving inside the modern roundabout have the right of way. This means that motorists trying to merge with circulating traffic must yield.

MODERN ROUNDABOUT ANIMATIONS

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.

Did you know . . . modern roundabouts can significantly reduce fuel consumption?

THE SUCCESS OF MODERN ROUNDABOUTS
Several studies have shown that modern roundabouts, a new form of traffic management, are successful in promoting safety.
Modern roundabouts are not the solution to traffic problems at all intersections or interchanges. However, replacing some traffic signals with modern roundabouts can reduce the likelihood and severity of rear end crashes by discouraging aggressive drivers. Due the low entry speed (15-25 mph) in modern roundabouts, motorists have no incentive to speed up when approaching green lights. Nor do they have any reason to slow down abruptly at red lights.
A 2001 Insurance Institute for Highway Safety study of 23 US intersections reported that converting intersections from traffic signals or stop signs to modern roundabouts reduced injury crashes by 80 percent and all crashes by 40 percent.

Replacing signals or stop signs with modern roundabouts can also significantly improve traffic flow. A study of three locations in New Hampshire, New York State and Washington State reported an 89 percent average reduction in vehicle delays and a 56 percent average reduction in vehicle stops.

Because modern roundabouts improve the efficiency of traffic flow, they also reduce vehicle emissions and fuel consumption. Studies have found that constructing modern roundabouts in place of traffic signals can reduce fuel consumption by approximately 30 percent. At 10 intersections studied in Virginia, savings added up to more than 200,000 gallons of fuel per year.