By: Eliana Zhang
“Every accident is a notice that something is wrong with men, methods, or material. Investigate, then act.” - Safety saying, circa early 1900s
The streets you drive on are dangerous. If you’re between the ages of 5 and 29, you’re more likely to die in a road traffic crash than anything else. Working to improve them is a slow and tedious process too! Road designs for mass transportation have countless factors that need to be considered, including fluctuating populations, traffic levels at varying times, road construction, road conditions, budgets, weather, and -- perhaps the most relevant of all -- the accidents that make streets so dangerous in the first place.
In the United States, more than half of the combined total of fatal and injurious car crashes occur at the 300,000 existing signalized intersections. This is not a surprise to engineers. When two two-lane roadways intersect, there are thirty-two opportunities for drivers to collide into each other, and the number increases the more complex your roads get. The effective, albeit bizarrely-designed, “diverging diamond interchange” (depicted on the left) and many other types of intersections have been considered to allow for safer and smoother flows of traffic. The prevailing form of roadway intersection, however, remains the standard signalized one, where traffic signals and painted lines ensure that streams of traffic are directed where they need to go. There is one alternative to traditional intersections already gaining popularity in Europe: the roundabout, otherwise known as the traffic circle, the rotary, or the island, depending on where you live. So why is America so hesitant to embrace it?
“[Clark Griswold is driving around Lambeth Bridge Roundabout in London, England, and is unable to turn to the left] Hey look kids, there's Big Ben, and there's Parliament... again.” - National Lampoon's European Vacation (1985)
The primary type of roundabout is the modern roundabout, designed to accommodate vehicles of all sizes. This is the form of roundabout generating the most attention from both supporters and skeptics. Drivers yield to traffic at entry, travel counterclockwise around a center island, and later exit at their desired street. There are no traffic signals involved. The following image is a modern roundabout in Barcelona, Spain, and it might look familiar to you.
The implementation of these roundabouts is built on three key pillars: efficient and satisfactory service as a traffic control system, the protection of travelers from potential injury, and the promotion of a prosperous economy. Critics of the modern roundabout say it increases travel time, confuses drivers, and wastes resources like land and money. Proponents, on the other hand, assert that it moves more traffic than a standard four-way intersection and only requires a small adjustment period for drivers. Under all this scrutiny, how does the modern roundabout actually fare?
1. Service:
Because cars must slow down while navigating a roundabout, it may seem like it’ll take longer for cars to get through the intersection. Contrary to this perception, statistics say roundabouts move 50% more traffic than traffic lights. With a continuous flow of traffic, drivers don’t have to wait for a green light to pass, and the intersection can handle more traffic in the same amount of time. Studies by Kansas State University also suggest that roundabouts provide less congestion for approaching roads. While measuring traffic flow at intersections before and after conversion to roundabouts, researchers found that in each case, the roundabout led to a 20% reduction in delays. Additional studies by the Insurance Institute for Highway Safety (IIHS) determined that roundabouts contributed to an 89% reduction in delays and 56% reduction in vehicle stops.
Make no mistake: roundabouts promote efficiency and are a great alternative to signalized intersections. Still, they only work as well as they do when traffic is moderate to light. When traffic is heavy, problems can arise. A document outlining Los Angeles’s roundabout policy from 2007 acknowledges that heavy traffic volume brings an increase in the needed diameter of the roadway, which in turn leads to higher speeds, less safety, and reduced efficiency.
There is one other problem. Engineers must take into account the reactions of individual drivers, and many Americans feel anxious about driving through roundabouts. A survey on drivers’ views of roundabouts conducted by the IIHS showed that only 31% of drivers were in favor of roundabouts, while 41% strongly opposed it. However, while most drivers panic at the idea initially, follow-up surveys done after a roundabout was installed demonstrate that after drivers actually use them, those who favored roundabouts increased to 63%, while those who strongly opposed them dropped to 15%. The reasoning was that drivers preferred traffic signals and stop signs until they realized roundabouts allowed them through the intersection safely and without having to stop. Favorable opinions on roundabouts clearly rise after continued use.
Roundabouts can provide efficient service and are a viable replacement for many signalized intersections on that basis. Both sides of the roundabout discussion agree they work well where traffic is reasonably light and drivers are familiar with the concept.
2. Safety:
Although driving in a roundabout isn’t very difficult when done correctly, many drivers still get confused, which poses a danger. Some may aggressively brake before entering or fail to yield to traffic already in the intersection; others stop in the circle thinking they should yield to those trying to enter. These are all possible collisions waiting to happen, and statistics show they happen often.
Given that vehicles must slow down while entering, though, roundabouts still help reduce the likelihood and severity of collisions. Speeds in a roundabout are typically between 15 and 20 miles per hour, meaning that the few collisions that occur are mostly minor. Furthermore, the roundabout makes all the traffic one-way: roads entering the intersection are gently curved to direct drivers counterclockwise. This all offers no possibility for ninety-degree or head-on collisions and reduces the number of conflict points between road users. According to studies by the IIHS and the Federal Highway Administration (FHA), roundabouts typically reduce overall collisions by 37%, injury collisions by 75%, and fatality collisions by 90%. It is unarguable that roundabouts are less dangerous than signal-light intersections for motorists. When properly designed with sidewalks on the perimeter, they are safer for pedestrians as well.
Roundabouts are not, however, all that safe for cyclists, which is especially relevant in a world with international pressure to bike more and drive less. A literature review conducted by Utah State University considered dozens of papers on how roundabouts affect cyclist safety, and it found that roundabouts may actually increase bicycle crashes, especially those with on-roadway bike lanes or no bicycle facilities at all. In one instance, a 2008 study of 91 roundabouts in Belgium demonstrated that roundabouts led to a 27% increase in “bicyclist injury collisions” and an increase of more than 40% in the number of fatal or serious injury cyclist crashes. Another study made in Denmark found that installations led to a 65% increase in bicycle crashes and 40% increase in injuries. Roundabouts do not always pose a danger to cyclists though! The same review adds that they can be safer for cyclists if they have low-speed traffic at a low volume, fewer lanes, larger and higher central islands, and separated bicycle facilities. This way, cyclists won’t be in danger of entering-circulating crashes, where motorists fail to keep an eye out for cyclists while entering or exiting the roundabout.
The protection that roundabouts provide for streets is not a large debate: everyone agrees that when people know how to navigate it, roundabouts are safer for motorists and pedestrians, but are more dangerous for cyclists in general. Critics contend that even with the safety they bring to motorists, the circular intersections represent the world’s overreliance on cars. Towns that reject the roundabout do not do so out of ignorance over the benefits the design brings to commuters-- the safety they bring to motorists should not be downplayed but the topic of discussion is turning to how the government may change commuting for the sake of the environment.
3. Economically:
According to the Washington State Department of Transportation, building a roundabout and building a traffic-signal intersection both cost around the same amount of money. When long-term costs are considered, roundabouts do not have the hardware, maintenance, and electrical costs that traffic signals require, which means that roundabouts can save cities between $5,000 and $10,000 per year. They can also work during power outages and do not require police to direct traffic. Although a roundabout needs more land for the intersection, the streets approaching it usually require fewer lanes and less space due to its efficiency with traffic.
When it comes to replacing pre-existing junctions, though, altering even a single four-way intersection into a roundabout has unique economic challenges. Because the actual roundabout requires more real estate, obtaining the physical space may prove to be difficult. If building the roundabout requires altering the landscape, then things like demolition, elevation, and resurfacing increase the cost of installation. Converting a traditional interchange also means moving the entire existing structure and rebuilding everything, which takes time… which in turn, reinstates the problem of traffic control; if you close down a major intersection, you need to provide drivers with an alternate way to their destination! With an unsatisfactory detour, people will, of course, find a different route, which will lead to cars commuting in areas that were not meant to support a high volume. At the end of it all, a single road closure can create a cascading effect on other traffic routes. Furthermore, commercial problems may arise from altering an intersection-- close a road for too long, and people will avoid driving there. Nearby businesses like restaurants and gas stations will take a severe hit.
In the end, the economic consequence of installing a roundabout depends on the unique circumstances of each junction. It can both be cheaper and more expensive than using a signalized intersection, so it must be considered on a case-by-case basis.
Given all the stated benefits, why is America so hesitant to embrace the roundabout?
It is true that many American towns are beginning to utilize these circular intersections, but the prevailing type of junction is, and will most likely continue to be, the traditional signalized one. The facts are that roundabouts are only effective in areas with a moderate amount of traffic, are safer for motorists and pedestrians but more dangerous for cyclists and are expensive to use as a replacement for pre-existing four-way intersections. But although roundabouts may not be used everywhere, you should expect to see more of these intriguing pathways in the near future. If you ever happen to be in control of a vehicle, I hope you will navigate one safely.
What did you learn?
Is a roundabout safe? A roundabout is definitely safer than four-way traffic-light intersections-- provided you’re a motorist or a pedestrian who knows how to use it. Some drivers may be concerned about navigating it for their first time, which is understandable, but roundabouts reduce the amount of conflict points between you and other drivers by steering vehicles through gentle curves in one direction. It offers less possibilities for injury or death no matter how confused you are while driving! If you’re a cyclist, roundabouts can actually be even more dangerous for you, so you’ll want to steer carefully and hope that the roundabout has separated bicycle facilities before entering one.
Is a roundabout a waste of money? Sometimes! Sometimes it’s not. A plethora of factors must be considered before deciding to spend thousands on a roundabout at a particular intersection. Large amounts of traffic or giant trailer-trucks passing through often are qualities that would not mesh well with a roundabout, so if a roundabout is installed in areas with those, it will not function as effectively as it could. Sometimes, though, installing and maintaining a roundabout is even cheaper than installing and maintaining a traffic-light intersection. Again, it depends on the particular intersection: it has the potential to be both good and bad.
Citations:
Image credit:
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