The big idea for this podcast is to discuss roundabouts, including their history, myths, pros, and cons.
(Photograph by Brian McGuckin, Courtesy of the City of Carmel, Indiana)
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Outline and Notes of the Podcast Discussion
For many of us roundabouts are every-day encounter. I navigate two of them pretty much every morning to take my children to school when I travel by car or bike. Oddly, they are also one of the only traffic devises or road design features with which drivers have a love/hate relationship. I often here a visceral…emotional response them them. "I hate them!" "Worst think ever!" "Best invention ever!" "I am scared of them and scared I will miss a turn. "They are so European!" Why is this? We discuss this question and many others surrounding roundabouts in this episode.
The predecessor to the modern roundabout, the traffic circle, was made famous by the National Lampoons European Vacation where the Griswold family gets stuck in a traffic circle in London...endlessly circling for hours. The hilarious scene seemed to captured several generations feelings on them. In this episode we will explore roundabouts including:
- The history of traffic circles and roundabouts
- Comparing the first versions (traffic circles) to the modern roundabout
- Roundabout myths
- Features of the modern roundabout
- Pros and Cons of the modern roundabout
History
The first traffic circles (aka rotaries) appeared in the early 1900s and functioned more like a circular road than an intersection. Columbus circle in NYC, Dupont Circle in Washington DC, and the Arc De Triumph in Paris are well-known examples. Many had signals and stop signs in the middle of the circle. Most drivers found them confusing and dangerous to navigate and by the 1950s construction on new traffic circles ceased world-wide. In 1966 Frank Blackmore, a civil engineer and former RAF pilot, who served in WWII, developed the “priority rule” or “give-way rule" which gave birth to the roundabout. The priority rule simply means that traffic entering the roundabout yields to traffic in the roundabout. It is hard to imagine navigating a roundabout today without this basic rule!
There are about 7,000 roundabouts in the US presently. By contrast there are approximately 300,000 signalized intersections in the US. Those opposed to replacing traditional intersections with roundabouts or using roundabouts for newly constructed intersections tend to rely on a couple of myths.
Top Three Myths
1. They are to large and thus won’t fit in tight spaces with established right of ways - They about the same size or smaller than signaled intersections mainly because they don’t require the turn lanes of a lighted intersection. Typically dimensions of the diameter of three different size traffic circles are below.
- Mini-roundabouts 45-90ft
- Single lane 90-180ft
- Multi-lane 300ft
2. They are dangerous – People don’t know how to navigate them so accidents are more common and definitely not safe for pedestrians. This myth is founded in US driver unfamiliarity with roundabouts with some availability heuristic mixed in. The human mind defaults to the status quo and we form an opinion on based on what information is available. Fewer interactions with roundabouts and some common cultural references result in a tendency to have a negative opinion of them. In places where roundabouts were built, public acceptance was often ~30% before implementation and ~70% a year after construction...thanks to increased familiarity. Furthermore, in a bit of irony, the reason why many don’t like roundabouts is a major reason they are safer. The unfamiliar forces us to focus and shift out of autopilot as we drive. This added focus is vital as a majority of driving accidents are caused by driver error, specifically in attention and distraction.
3. They slow down traffic. Yes, they do force traffic vehicles to slow as they approach and navigate the roundabout by constricting the driving space and adding angles. This is one of the major safety features as slower traffic leads to less injury causing accidents. However, while they slow individual cars traversing the roundabout, they actually improve traffic flow and throughput by 30-50%. It is difficult to perceive this benefit at the individual driver level because you feels like it slows you down but if your overall drive time is the same or less than with a signaled intersection.
Pros
- Safer: less crashes and less severe injuries
- Less stopping
- Less fuel use by vehicles
- No electricity required to power traffic lights
- More bike and pedestrian friendly
Cons
- Not appropriate for all intersections, particularly: dense urban intersections or interstate highway intersections
- Not compatible when mixed in traffic signals that rely on "platooning" (grouping of cars to move through several lights in a row) common in many areas
- Not familiar to many drivers
- Careful design required in order to accommodate trucks with long turn radiuses
Yes it is possible to go a bit overboard. Checkout this roundabout of roundabouts located in the town of Swindon in the UK. There are six roundabouts and 38 arrows that form this intersection of five roads.
References
"Modern Roundabout Boost Traffic Safety and Efficiency" by Robert L. Reid for the March 2021 issue of ASCE magazine. We made several references to the article during this episode. There is lots of great information in the article for further reading on roundabouts.
"Car Crash Mystery: Why Can't Drivers Figure Out Roundabouts?" by Scott Calvert in the Wall Street Journal newspaper on 14 March 2020.
Threads to pull for future episodes
- Sneckdowns or snow-neckdowns
- Traffic calming
- What other everyday infrastructure components would you like us to discuss in future episodes? Send us an email with suggestions.
Podcast Hosts
Jason Toth, P.E., PMP and Scott Snelling, P.E.
To provide comments, contact the hosts on Twitter at @jasontoth_pe and @snellingscott or on LinkedIn at jason-a-toth and scottsnellingpe.
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