Roundabouts & Squareabouts

Roundabouts and Squareabouts

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A roundabout – AKA rotary, traffic circle, or road circle – is a type of a intersection where multiple roads converge, like the spokes on a wheel, onto a central hub. Each car enters the hub, travels in a standardized direction around a central island, and exits the circle onto its chosen road. Although this traffic device has been used around the world for centuries, it is relatively new to North Carolina’s roads, and the roundabouts that are proliferating around our state seem to trigger acute anxiety in many drivers as they approach one. But with anxiety comes heightened awareness, and that is part of the secret behind roundabouts saving lives.

Roundabouts – A modern version of an old concept

Circular road junctions have been used to control traffic flow for at least hundreds of years. In Bath, England, a circular junction called “The Circus” was completed in 1768. And in the United States, in 1821  Indianapolis, Indiana created a traffic circle called “The Governor’s Circle” (later renamed “Monument Circle”), thus gaining the city the nickname of “The Circle City.” The first traffic circle in America designed for the automobile was Columbus Circle in New York City, built in 1905.

The Circus, Bath, England
The Circus, Bath, England
Monument Circle, Indianapolis
Monument Circle, Indianapolis
Columbus Circle, New York
Columbus Circle, New York

All three rotary junctions mentioned above are, properly speaking, traffic circles as opposed to roundabouts. The general distinction is that traffic circles are typically large in scale and multi-lane. Vehicle flow is often controlled by traffic lights, sometimes requiring cars already in the circle to yield to those entering it. Traffic speed can be relatively fast. A roundabout is a smaller version of the circular configuration. They frequently consist of a single lane of traffic, and cars entering the circle always yield right-of-way to cars already in the circle. Traffic flow is not controlled by lights or stop signs, and speeds are low, especially with cars entering the circle. In North Carolina today, we have roundabouts rather than traffic circles.

The modern era of the roundabout began in the 1960s, when the United Kingdom began constructing single-lane rotaries with the standard convention that vehicles entering the circle must yield to vehicles already in the circle. (Of course, being the UK, traffic flow around the circle was clockwise instead of the counter-clockwise flow in US roundabouts.)

The modern roundabout arrived in North Carolina in 1999, when the NC Department of Transportation installed one in the town of Clemmons.

A simple, one-lane roundabout
Clemmons, North Carolina

Roundabouts versus Intersections

At the most obvious level, traditional intersections and roundabouts differ in their shape. At a typical traditional intersection, two roads simply cross each other, with the flow of traffic through the intersection controlled by either stop lights or stop signs. A roundabout is essentially a loop around which all traffic from the converging roads travels in one direction. In the United States, that direction is always counter-clockwise. Roundabouts are typically circular with a raised central island, but they can be oval or even irregular shapes, so long as they permit a continuous loop of traffic. A roundabout can be single-lane or multi-lane, but in North Carolina the vast majority are single-lane.

Animation of traffic navigating a roundbout
A roundabout in action

Roundabouts improve efficiency

Many drivers have the impression that roundabouts cause congestion, but traffic studies show that roundabouts can actually reduce delays by around 65 percent. The misunderstanding may result from drivers observing that vehicles approaching a roundabout always slow down, and that reduction in speed can cause the formation of a queue of cars wanting to enter the circle. That does often happen, especially at peak traffic times (roundabouts being most efficient at non-peak periods), but cars rarely come to a full stop in such a queue even in heavy traffic. They continue to move slowly forward toward the circle.

Contrast that to a standard intersection with a traffic light. As a car approaches an intersection, the light will be green only around part of the time. The for the rest of the time, the approaching car must come to a full stop at the red light. And even during the early part of the green phase, an approaching car will  frequently have to slow down because of the backup of cars that had stopped for the previous red light. The efficiency of a light-controlled intersection is further reduced by what engineers call the “clearance phase” – the brief period when all lights show red in order to ensure that the intersection is clear of cars and ready for traffic to enter from a different direction.

Roundabouts save lives

Motorists tend to feel comfortable at traditional – therefore familiar – intersections. Most of us have been negotiating this type of junction for years. But road crossings are extremely dangerous places: fifty percent of automobile crashes occur at an intersection. Traffic safety engineers use the term “conflict point” to identify likely places for an accident. The standard analysis of traffic flow at a hypothetical intersection shows a staggering 32 places at the intersection where two automobiles are likely to collide. By contrast, safety analysis of a roundabout show only 8 vehicular conflict points.

Diagram of the 32 conflict points in a traditional intersection
The 32 conflict points in an intersection
Diagram of the 8 conflict points in a roundabout
The 8 conflict points in a roundabout

The key to the difference in conflict points lies in the concept of deflection. By deflecting traffic from a straight-line crossing – that is, by routing it on a curved path around the circle – the roundabout eliminates the two most dangerous situations at an intersection. The first of those situations is when a car crosses the intersection at high speed, thus exposing it to the danger of a t-bone crash with, for example, an automobile crossing its path after running a stop signal. The second is when a driver uses the intersection to turn left, trying to time their move with a gap in oncoming traffic. For a driver making such a left turn, the line of sight to oncoming thru traffic is often blocked by cars waiting to make their own left turn across his/her own path.

Given the potential for a collision at an intersection, you might hope that drivers would approach the crossing with with their attention focused on other cars, and that they would approach with some caution. But the reality is that many drivers approaching an intersection focus their attention not on oncoming traffic, but on the traffic light itself. And they may actually speed up in an effort to reach the intersection before the light changes.

A driver approaching a simple roundabout has no distracting traffic light, and they typically focus their attention on traffic to their left that is coming around the circle. They also invariably reduce their speed. Part of the slowing down is because it is required in order to navigate the circle. Part is because they will be merging with traffic in the circle that is also traveling more slowly. And part of the slowing may be because the driver is not as comfortable with a roundabout as with a traditional intersection, and they experience doubt and anxiety.

Slower speeds are fundamental

Slower speeds are an important component of traffic safety in general for the simple reason that they give drivers more time to react in unexpected situations. But in a roundabout, slow speeds are critical. In a roundabout, car drivers – and frequently bicyclists and pedestrians – are constantly negotiating for space in a constant ballet of merging and yielding. The key to this dance is eye contact among all parties, and a constant visual messaging along the lines of, “I see you.” “Go ahead.” “What are your intentions? “”I’m coming in there.” Communication by eye contact is not only a product of roundabout design, it is essential to the smooth flow of traffic in and around and out of the circle. And studies show that above a speed of 20 miles per hour, humans are not able to make eye contact with one another. So the slower speeds at a roundabout are a key component of the circle’s efficiency and safety.

Anxiety is not modern

Unease on approaching a roundabout is not necessarily a modern, auto-age phenomenon. In the Covent Garden section of London, seven roads converge on a traffic circle known as Seven Dials. Approaching automobiles invariably slow as they near Seven Dials, and so, apparently, did horse-drawn buggies long ago. Charles Dickens remarked on the atmosphere there in the 1830s in his Sketches by Boz:

The stranger who finds himself in the Dials for the first time…at the entrance of Seven obscure passages, uncerain of which to take, will see enough around him to keep his curiosity awake for no inconsiderable time.

An etching of the Seven Dials intersection in London
The Seven Dials, London

Whatever the combination of factors, experience has shown that roundabouts are significantly safer than intersections, especially with regard to serious and fatal accidents. A 2020 report by The North Carolina Department of Transportation Safety Unit compared accident rates between 13 roundabouts and the intersections those roundabouts replaced. Their finding was that the roundabouts reduced total crashes by 41%, reduced front-impact (head-on) crashes by 62%, and reduced crashes with injuries or fatalities by 79%.

The roundabout is not a silver bullet.

It is worth noting that a roundabout is not necessarily a silver bullet. Their safety relies on the drivers who use them obeying norms of use. Many of the accidents that do happen occur when drivers entering the circle fail to yield to traffic already in the circle, or when drivers navigating the circle unexpectedly brake for entering traffic. With a multi-lane roundabout, confusion about how to exit can cause novice users to change lanes while in the circle – a big no-no with roundabouts. 

A locally infamous example of this problem was seen in the original circle at Hillsborough Street and Pullen Road in Raleigh. While the roundabout was a success in reducing serious accidents at a historically dangerous intersection, it produced a higher-than-expected number of fender-benders – 132 in its first two years of operation. Traffic engineers determined that the high accident rate in the multi-lane roundabout (one of only three in the state) was the result of driver confusion over which lane to use in order to be able to exit on the road they wanted. That confusion led to frequent in-circle lane changes and cars bumping into each other. When the roundabout was redesigned as a single-lane circle, the accident rate plummeted.

The Squareabout - a round peg in a square hole

From the design standpoint, the common wisdom has long been that circular roundabouts do not fit well into the typical urban cityscape, with its streets and buildings rigidly set in a rectilinear grid. But in the year 2000, the City of Drachten in the Netherlands found a solution to that conundrum when it redesigned an existing major city square and traffic intersection known as the Laweiplein. Their solution was to continue to embrace the original square plaza and simply to superimpose on it a single-lane roundabout. Traffic engineer Hans Monderman, the creative force behind this merging of geometric forms, called his solution a “squareabout.”

An aerial view of the Laweiplein squareabout
The Laweiplein squareabout

With the new design, gone is the visual clutter of traffic lights, light poles and wires, and directional signs. And the Laweiplein has become a vibrant shared space for motor vehicles, bicyclists and pedestrians. The circle is devoid of virtually all road markings, including bicycle lanes, so bicyclists use the entire road. Motor vehicles and bicycles navigate the circle at approximately the same sedate speed, and even pedestrians find crossing the circle to be non-threatening, often waved on by deferential drivers. There is a constant eye and hand-signal communication among participants to sort out what is really a transportation ballet.

Bicycles and autombiles share the Laweiplein.
The Laweiplein is a shared space.

The Laweiplein is a real-world validation of Hans Monderman’s inspiration that a “shared space” – in which there are no artificial barriers segregating motor vehicles, bicycles and pedestrians – is safer for everyone. And his squareabout is also more efficient. At times of peak traffic, a line of vehicles may approach the circle slowly, but the line rarely stops. And average times to navigate the roundabout are far lower than they were when it was a cross intersection. With the old intersection, buses carried transponders that gave them priority at the traffic lights, and yet the roundabout has dropped their average rush-hour crossing times by as much as one half. And accross-the-board average crossing times have dropped from 50 seconds to 30 seconds.

The bottom line

So the next time you approach a roundabout in your car, go ahead and be a little anxious. Slow down, and look to your left for traffic already in the circle. Yield to those cars, then enter the circle, and be on your way. You just navigated one of the safest, most efficient, and least visually cluttered places on the road.

Click this link for a video of the Laweiplein squareabout in action.

Here us a link for advice from the North Carolina Department of Transportation on how to use a roundabout.

The NCDOT 2011 report “Safety Evaluation of Roundabouts in North Carolina” 

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