American drivers should learn to love the roundabout.

How we get from here to there.
July 20 2009 6:54 AM

Don't Be So Square

Why American drivers should learn to love the roundabout.

Illustration by Robert Donnelly. Click image to expand.

Here is a narrative that has been playing out over the last several years in any number of American towns: Traffic engineers notice that a particular intersection has a crash problem or is moving traffic inefficiently. After a period of study, the engineers propose a roundabout. The engineers, armed with drawings and PowerPoint slides, visit a community meeting. They try to explain the benefits of their proposed design in clear language, though they may occasionally drop phrases like entry path overlap or inscribed circle diameter. Townspeople raise concerns. Roundabouts are not safe, they say. They are confusing. They are bad for pedestrians. They will hurt local businesses. They are more expensive than traditional solutions. The local newspaper reports this, adding some man-in-the-street comments from "area drivers," who profess not to like roundabouts, even making dark references to "circles of death." Then, the roundabout is built, the safety record improves, traffic congestion doesn't seem any worse than before, and the complaints begin to fade faster than white thermoplastic lane markings in the heat of summer.

According to best estimates, the United States is now home to about 2,000 "modern roundabouts"—more on that phrase in a moment—most of which were built in the last decade. As engineer Ken Sides noted in the ITE Journal, however, in 2008 Australia built its 8,000th roundabout; by Sides' calculation, the United  States would need to build roughly 148,519 more roundabouts to match the Australian rate per capita. Interestingly, Australia—a country whose traffic landscape is rather similar to ours—has, since 1980, cut its traffic-fatality rate to nearly half the U.S. figure. The rise of roundabouts has no doubt played some part.

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Why are Americans so suspicious of roundabouts? The simplest answer is that we have grown used to (and feel comfortable with) binary, on-off traffic control. We suspect such signals are more efficient than the "fuzzy logic" that seems to govern roundabouts. Roundabouts require drivers to make their own decisions and assess others' actions, rather than relying on third-party signals.

But psychology offers a few interesting clues as well. Mentioning roundabouts seems to invoke some form of the famous "availability bias," which leads people make judgments based on the memories that can be brought most easily to mind. And so, the American who may have driven as a tourist in France or Greece a number of years back will shudder with recognition, associating the roundabout with terror and near misses. But motorists with such memories often fail to consider that they were driving as tourists in unfamiliar climes, perhaps only for a few days. Roundabouts, like the language, the signage, the food, and just about everything else, were strange and novel, and so the tourist driver, already probably feeling a bit wigged out—for a roundabout in Italy is filled with Italian drivers—felt a heightened level of stress and thereafter consigned the roundabout to the dustbin of terrible ideas—or things that might be good for Europe (like socialized medicine) but don't translate.      

Another problem is that the word roundabout brings up for many people an image of an old "traffic circle" or, in the Northeast, a "rotary" intersection. But these are not necessarily roundabouts, just as the Arc de Triomphe is not a roundabout, nor is New York City's Columbus Circle (which, for the record, is acknowledged as the world's first "rotary system" intersection).

The two are fundamentally different beasts. You are in a modern roundabout if it is the entering driver who must yield to traffic already circling. You are not in a modern roundabout if you are expected to yield to entering drivers or if you encounter traffic lights or stop signs. Size is another easy distinguishing mark. The old traffic circles were huge, and actually required drivers to make fairly significant detours around a vast central area—typically just an expanse of desultorily tended grass. Roundabouts are typically half the size; some, like one in Kingston, N.Y., were built inside the infields of existing traffic circles. Rather than simple lawns, their centers may contain statues, beds of flowers, or any number of visual elements. Velocity is another telltale identification mark. The older traffic circles are often marked by high "entry speeds"—drivers come blazing in on long arcing curves and must then merge, highway-style. In the tighter spaces of the modern roundabout, the entrances and exits are "flared" with "splitter islands" that "deflect" incoming traffic.

This confusion is likely to last as long as these older circles are still in the landscape. But as modern roundabouts begin to appear with increasing frequency, here are a few reasons to be cheerful, which I have arranged in the easy-to-remember acronym STEP:

Safety. Intersections are perhaps the single most dangerous environment in traffic. According to the Federal Highway Administration, more than one-fifth of all traffic fatalities happen at intersections. If you think the problem is a lack of signals, think again. Reports FHWA: "Only 10% of all intersections are signalized, but nearly 30% (2,744) of intersection fatalities occurred at signalized intersections."

Roundabouts are safer than traditional intersections for a simple reason: By dint of geometry and traffic rules, they reduce the number of places where one vehicle can strike another by a factor of four. They also eliminate the left turn against oncoming traffic—itself one of the main reasons for intersection danger—as well as the prospect of  vehicles running a red light or speeding up as they approach an intersection to "beat the light." The fact that roundabouts may "feel" more dangerous to the average driver is a good thing: It increases vigilance. It's unlikely the average driver killed or severely injured in a high-speed "T-bone" crash as they drove through a green light felt much risk. In addition, drivers must slow to enter a roundabout: Placing an obstacle in the center makes this not only a physical necessity but visually disrupts the speed-encouraging continuity of the street. Motorists also travel through a roundabout more slowly than they would a traditional intersection: Roundabouts are typically built using what's called "negative superelevation," meaning that water flows away from the center and also that the road slopes against the direction of a driver's turn. As a result, any crashes in a roundabout take place at lower speeds and are thus less likely to be fatal. While roundabouts can be more costly to install than other kinds of traffic controls, such calculations don't take into account the fact that reducing fatal crashes also reduces social and monetary costs.

Time. People may see vehicles winding slowly through a roundabout and think the intersection must be 1) adding to congestion and 2) slowing down people's travel times. But travel speed at any given moment should not be confused with overall travel time. Drivers may breeze through one intersection's green lights only to sit through a 90-second cycle at the next. What's more, the "protected turning movements"—i.e., the green arrows—required at many intersections steal time from the larger numbers of people wanting to proceed in every other direction. Roundabouts slow but rarely stop traffic. A noteworthy example here is Golden, Colo., which in 1999 converted a series of four formerly signalized intersections to roundabouts on a wide section of arterial highway that was becoming a major corridor for "big box" retail. While speeds between the intersections fell to an average of 37 mph from 47 mph, the time to travel the entire stretch of road dropped.

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