Thinking Round
Author’s note 12/11/22: As I would like this to be a living document on the benefits and features of roundabouts, and it has been over a year since this was first published, I’ve made a few edits to update the state of the practice.
As we enter the next and most crucial part of the 21st century, America is still grappling with problems that have persisted for decades. Transportation is one of the biggest sectors that has contributed to these long-term problems, but as Transportation Secretary, Pete Buttigieg has pointed out, transportation can also provide the solutions.
Federal, state and local agencies can promote and use transportation to solve many challenges such as: improving safety, creating equity, addressing climate change while being resilient against its effects, and bringing businesses and communities together to create that sense of belonging and economic opportunity, all while being prepared for the future of travel.
There is one transportation solution in particular that addresses all these areas, and that solution is found by thinking round.
More specifically, that solution is a roundabout.
I’ve written about them multiple times before, but this story will put all the benefits of roundabouts in one place to show how they can solve problems of today and tomorrow, and to hopefully convince readers of their worthiness and advocacy.
Round is safer for all users
According to the Federal Highway Administration (FHWA), roundabouts have been proven to have the following reductions in crash types after converting from stop-controlled and signalized intersections:
- 72–87% reduction of fatal and serious injury crashes
- 44-48% reduction in total crashes
Conversion from signalized intersections have had the most total crash reduction benefit (48%) while rural settings have had the largest fatal and injury crash reduction (87%).
In addition, PennDOT data from 22 roundabouts constructed from 2000 to 2019 that replaced signalized and stop-controlled intersections showed a 100% reduction of fatal crashes, with suspected serious injuries declining by 77%.
The majority of multi-vehicle crashes that do occur in roundabouts are typically low-speed, and due to the angle of entry, sideswipe crashes that cause damage to vehicles only. The lower number of conflict points for roundabouts — eight for a single lane — compared to 32 for a four-way intersection, also reduce the probability for crashes to occur.
Two examples of roundabouts improving safety can be found in my state in Kennebec County:
The first example is the conversion of Cony Circle in Augusta from a two-lane rotary (image above) to a multilane roundabout (image below). According to state crash data, there were 271 crashes in the three years prior to construction in 2009 with 58 injury crashes. In the three years that followed the conversion, there were 126 crashes with only 19 injury crashes. That’s a reduction of over 53% for total crashes and over 67% for injury crashes, clearly a major improvement in safety performance.
The second example is the construction of a single-lane roundabout that I designed in West Gardiner at the intersection of Route 9/126, I-95 Exit 109 and the Maine Turnpike Service Plaza.
This was once an intersection that had the highest crash probability in the state according to a 2013 article in the Bangor Daily News. The prior configuration was a two-way stop control on the minor legs with Route 9/126 having traffic that did not stop in a corridor with a speed limit of 45 MPH. Traffic would exit from the Maine Turnpike to the north and have to proceed south across Route 126 to enter the Service Plaza and vice-versa when exiting from it.
According to state crash data, there were 13 crashes in the three years prior to roundabout construction in 2015 with four injury crashes. In the three years that followed, there were five crashes with zero injuries. As of December 2022, there have only been ten total crashes since construction with only one injury crash. So far the roundabout continues to be a safety success story.
While we know roundabouts are safer for vehicles, various studies have also shown they are safer for vulnerable road users (pedestrians and cyclists) as well. Although there is no official national record of roundabout crashes, there are only seven pedestrian fatalities that have occurred at a roundabout in the United States since they were introduced in the late 1990s and there have been only four known cyclist fatalities.
Red-light running, which causes more than two deaths per day on US highways according to a study by the AAA Foundation for Traffic Safety, is not possible at a roundabout. Over five percent of red light running fatal crashes also involve pedestrians or cyclists.
Speed is obviously the biggest factor, as the higher the vehicle speed, the lower the chance of survivability if a person is struck by a vehicle. Bicycle and pedestrian crossings at roundabouts occur where vehicles are slowing on entry, or have not yet increased speed fully after exiting. Therefore, they typically have lower speeds than a crossing at a signalized intersection.
Distracted driving is another issue that has caused serious injury and death on highways in the United States. A 2018 study by the Risk Institute at The Ohio State University found in the data they collected from 2013 to 2017 that roundabouts reduced fatal crashes due to distracted driving by 100%, and were the most effective traffic control countermeasure to distracted driving that could be constructed.
Based on these examples and sources, if increasing user safety is a goal, roundabouts have proven that they are a solution for all users.
Round is equitable
Secretary Pete surprised many people with one exchange in an interview for Axios on HBO and this accompanying tweet:
Equity in transportation for all users is something that has been missing from a national perspective. “Accommodation” was always the term that has been used in the past, but equity and accommodation are two different things. To have accommodation in transportation means that an asset is built primarily for vehicle use. Equity means it is built for all users, especially and they are integrated into the system.
When he was mayor of South Bend, Indiana, Buttigieg implemented a “Smart Streets” initiative that attempted to create equity among all road users — vehicles, cyclists and pedestrians — for certain streets in South Bend. Roundabouts were a key part of this initiative as they increased the safety of vulnerable road users by lowering speeds and providing facilities for safe travel.
Pedestrians can choose when they want to safely cross at a roundabout (with pedestrian facilities), unlike at a signalized intersection which gives priority to vehicles. Most states (save for Oregon and South Dakota which defer to local ordinances) also require vehicles to either yield or stop to a pedestrian in a marked crosswalk without signals.
Roundabouts also automatically provide refuge for pedestrians via their splitter islands, making each crossing a two-stage crossing, allowing pedestrians to rest in the island if they choose not to cross both sides of the road immediately. This certainly creates more equity for those with mobility issues. Pedestrians also only need to look in one direction when crossing, and have shorter crossings to make, unlike at signalized or stop-controlled intersections.
However, blind and visually impaired pedestrians have still had concerns about roundabout safety, as it is often difficult for them to determine circulating from exiting traffic. Engineers have discovered that utilizing raised crosswalks can both increase the yielding to pedestrians as well as decrease the amount of interventions needed by an accessibility specialist. The use of staggered offset-left crossings (shown below) can also allow a better audible determination of exiting and circulating traffic. Both of these solutions have been utilized in recent roundabout designs and are planned for future roundabouts to increase the safety of blind and visually impaired users.
Pedestrian hybrid beacons (PHB) and rectangular rapid flashing beacons (RRFB) with accessible pedestrian systems (APS) having audible messaging and locator tones have also been used in multilane roundabouts to improve yielding rates and to provide a better determination for when it is safe to cross. Vehicles are required to stop at a PHB when activated and in the solid or flashing red phase, while RRFBs, when activated, have a unique flashing pattern to alert approaching drivers that they will need to yield to crossing pedestrians.
Beacons with APS are also required for use at multilane roundabouts in the 2011 US Access Board’s Public Right-of Way Accessibility Guidelines, more commonly referred to as PROWAG by industry. PROWAG, however has yet to be adopted nationwide, but many states have still attempted to best implement its recommendations at roundabouts.
For cyclists, roundabouts provide the ability to share the circulatory roadway with traffic and/or provide bike ramps for navigation of users around the roundabout via a shared use path. The slower speeds and shared use in general make cycling in a roundabout a more pleasant experience than navigating in a bike lane at a signalized intersection surrounded by vehicles, especially once cyclists are used to roundabouts.
Here’s one cyclist’s take from an article giving tips about navigating a roundabout in The Clarion Ledger of Clarion, Mississippi:
…as a driver and a cyclist, I prefer navigating roundabouts to having to wait at four-way stops or traffic lights. I will never be accused of blowing through a stop sign, and I never have to wait for a traffic sensor to recognize my bike!
Round is green and resilient
Climate change is a major focus of the Biden Administration and Congress. With the passage of the Infrastructure Investment and Jobs Act (also known as the Bipartisan Infrastructure Law), as well as the Inflation Reduction Act, any transportation agency receiving federal dollars has needed to address climate change in some way, with both a reduction of carbon and other harmful emissions, and also creating infrastructure that is resilient to climate change.
Roundabouts are a perfect solution for both transportation agency challenges.
According to part of a FHWA report in 2015, compared with 42 signalized intersections, the 24 roundabouts that were studied had less emissions of nitrogen oxide (NOx), hydrocarbons (HC),carbon monoxide (CO), and carbon dioxide (CO2) on average than the signalized intersections for most periods of traffic.
The only time roundabouts had slightly higher emissions than signalized intersections were at peak or near peak traffic volumes with optimized signals. Once off-peak or surpassing peak design volumes for even optimized signals, roundabouts had the least amount of emissions generated for all pollutants but CO, where an optimized signal was only slightly better.
Quantifying these reductions at roundabouts compared to stop-controlled intersections, an earlier Kansas State University study found the following:
- 21–42% reduction in CO emissions
- 16–59% reduction in CO2 emissions
- 20–48% reduction in NOx emissions
- 18–65% reduction in HC emissions
In both studies, compared to signalized and stop-controlled intersections, roundabouts were able to reduce harmful vehicle emissions, which is crucial to the transportation sector’s ability to mitigate climate change.
Resiliency to climate change is also a strength of roundabouts, and Ken Sides, PE, PTOE, CNU-a, a fellow transportation professional and roundabout advocate, had an excellent article titled “Round is Resilient” in the October 2018 edition of the Florida Engineering Society Journal which gave examples of that benefit.
In the article, he points out the lack of electricity that is needed for a roundabout to function, compared to the absolute necessity for a signalized intersection. This allows roundabouts to function during and after extreme climate events which can render signals non-operational for days.
Sides also refers to roundabouts being used as temporary traffic control in Wilmington, North Carolina, when signals were non-operational after Hurricane Florence made landfall in September 2018. A Wilmington traffic officer had the idea to set up cones in the geometry of a single lane roundabout within a multilane intersection and saw that traffic flowed much smoother than when he was directing traffic. The cone roundabouts also only required three officers and a police car set in the middle instead of the 12 to 16 officers that were previously needed to direct traffic for 24 hours. The first installation worked so well that other non-operational signalized intersections in Wilmington were converted to “coneabouts.” The design has since been refined so it can be deployed for a future severe climate event if necessary.
Round creates belonging and economic opportunity
Transportation has the ability to transform communities, and roundabouts can be a catalyst for that transformation. With a roundabout, communities get a blank canvas to create their own unique identity.
Unlike a signalized intersection, roundabouts provide a central island and other spaces to create that sense of community and belonging through landscaping and art. These areas also serve a dual purpose for intersection visibility and also aid wayfinding for blind and visually impaired pedestrians.
State and other local agencies will usually try to minimize landscaping to lower maintenance work and costs, but communities have the opportunity to take on that work and costs themselves for a more defining design. Local garden clubs and art committees have held contests for landscape design and public art in and around roundabouts and have allowed the residents to have input to determine the winners.
While there needs to be safety considerations for errant vehicles when it comes to what is placed in a roundabout central island, especially in high speed locations, there are plenty of landscaping options as well as crash-forgiving art materials for placemaking.
Roundabouts also provide economic opportunity as businesses are attracted to areas that have good traffic flow and are safe and friendly to all users. As mentioned earlier, roundabouts create that sense of community and belonging where vulnerable road users will want to be.
A good example of economic prosperity due to roundabouts is in Golden, Colorado, where one of the first roundabout corridors in the US was constructed from 1998 to 1999 on South Golden Road.
Before the roundabout installation, South Golden Road was a four-lane highway with a two-way left turn lane and wide shoulders. There were some sidewalks, but crossings were extremely long and especially difficult for those with mobility issues. It was not considered to be a pedestrian friendly environment. The city decided to install the roundabout corridor to make the area safer, more pedestrian friendly, and aesthetically pleasing.
In a 2004 report titled “Are Roundabouts Good for Business?” the author, Alex J. Ariniello, stated that in the six years after roundabout construction, sales tax receipts along the corridor in Golden grew 60% and 75,000 square feet of new retail/office space had been built.
Another project which included roundabouts, Mayor Pete Buttigieg’s Smart Streets initiative for South Bend, also spurred growth with more than $100 million dollars of private investment according to an article in the South Bend Tribune.
Given these two examples, the answer to the previous question is clear:
Roundabouts have been proven to be good for business and creating economic opportunity.
Round is ready for the future
“Smart signals” with the ability to interact with vehicles are being installed all across the country. These signals have equipment that will eventually communicate to vehicles using new 5G cellular data streams with vehicle-to-infrastructure (V2I) technology.
While this technology should help with traffic flow and safety, connected vehicle technology also keeps changing, so eventually it will need to be upgraded in the signals that are currently being installed. It is also extremely fragile and will be increasingly expensive to replace if damaged by severe climate events.
Roundabouts don’t require any special equipment and instead will rely on vehicle-to-vehicle (V2V) technology which will automatically be upgraded as vehicles are. Therefore, they are already connected and autonomous vehicle ready.
Roundabouts will not only be able to function in the interim as connected and autonomous vehicles enter the mainstream, but will also function well into the future without the need for expensive upgrades, or repairs due to climate events.
Barriers to “thinking round”
Currently it is estimated that there are almost 9000 roundabouts in the United States, but with this country’s vast network of highway miles, that fails in comparison to countries like France and the United Kingdom. The number of US roundabouts is also far less than the approximate 300,000 signalized intersections that currently exist.
Here’s another fun fact from Ken Sides’ article referenced earlier: to reach a similar number of roundabouts per capita as France, the US would need to construct over 140,000 more roundabouts.
Our country will likely never have that many roundabouts, but the pace of roundabout construction has also slowed according to a report from the Roundabout Database by Kittleson & Associates.
The report shows there were 574 roundabouts constructed in 2018, a high point, then 521 reported in 2019, 499 in 2020, and only 383 built in 2021. If that number holds as more reports come in and are verified, that would unofficially be the lowest number of roundabouts built in the US since 2012.
So why has the pace of roundabout construction slowed?
Cost is probably the biggest factor, as most roundabouts require closed system drainage with underground pipes and catch basins to collect stormwater due to all of the curbing that is part of the traffic calming aspect. The grading of roundabouts usually also requires significant excavation and replacement of road base gravel.
Roundabout projects are also not a favorite of the contracting industry because of perceived and actual challenges in construction. That lack of project preference also typically leads to higher bid prices.
However, just like any other type of construction, as more are constructed, contractors will continue to develop methods to make roundabout construction easier and more efficient, and bid prices will drop. Also, with the further development of machine control construction methods including universal 3D and 4D models, all highway construction projects, including roundabouts will only continue to become easier to build in the future.
Getting back to cost, too often only the up-front design and construction cost of a roundabout is considered, but consider the economic cost per type of crash as determined by the National Safety Council:
Average Economic Cost by Injury Severity or Crash, 2020
- Death (K) — $1,750,000
- Disabling (A) — $101,000
- Evident (B) — $29,200
- Possible (C ) — $23,900
- No injury observed (O) — $12,800
- Property damage only (cost per vehicle) — $4700
Now also consider the earlier figures for roundabouts with reduction of crashes and crash severity, and the fact that out of 40,000 deaths on US highways, around 20% of those occurred at intersections.
That means there’s not only the potential of saving thousands of lives, but billions of dollars in economic cost by significantly increasing roundabout use over signalized and stop-controlled intersections.
The average roundabout will have paid for itself well before its typical 20-year design life is completed with reduction in crash costs alone, while a signalized intersection does not offer the same safety and economic benefit. A fatal collision, or multiple serious injury collisions at a signalized intersection, could in fact make the ending result more costly than the signalization project itself, in addition to the routine maintenance costs of the signals.
So it’s clear, while roundabouts do have an up-front cost that is greater than other intersection control, they offer the greatest overall economic savings from crash reduction and severity of crash reduction.
Factor in the environmental benefit, climate resiliency, increase in user equity, overall economic development benefit and community placemaking, and future adaptability to connected and autonomous vehicles, roundabouts overwhelmingly are a worthy investment of transportation dollars compared to other types of intersections.
If they clearly are an excellent investment, what are the other reasons more roundabouts aren’t being built?
Education and enforcement, or the lack there of, are the other key factors to why roundabouts don’t have universal acceptance and implementation similar to a traffic signal. However, both are cheaper to address with national efforts rather than building more signalized or stop controlled intersections, and potentially having multiple serious injuries or loss of life occur at them, in addition to the inequity and increased vehicle emissions.
FHWA has the ability to use its resources as well as the Transportation Secretary himself to create a national campaign to raise awareness of roundabouts and their benefits, as well as stating the common myths and why they aren’t true. Such a campaign could also be taken up by state DOTs and local agencies.
FHWA could also make roundabouts the preferred type of intersection at the federal level instead of just an alternative to a signal or stop-controlled intersection, as multiple states have already done. States would then be required to justify any other type of intersection control to be built. This would also require agencies who are not as familiar with roundabouts, to become educated about their benefits and potential economic cost savings, instead of choosing not to build them because of a lack of familiarity or preference.
Lastly, the Secretary can push for funding a Uniform Traffic Code to be issued, as the Uniform Vehicle Code was last updated in 2000, well before the mass implementation of roundabouts in the US. The Uniform Vehicle Code was also not written with equity for vulnerable road users. A Uniform Traffic Code would allow states to adjust their traffic laws to match, giving law enforcement the tools to consistently and correctly enforce proper roundabout operations from state to state, and to ensure equity for all users.
Final thoughts
After reading all this, hopefully I’ve made a convincing argument that “thinking round” and dramatically increasing roundabout construction in the United States is something that we must do. The current priorities from Congress and the Biden Administration line up perfectly with what roundabouts can provide, so now is the time to act.
Regardless if you are convinced or not, here’s an exercise that I would encourage all readers to do:
First, locate your nearest roundabout. Use the Roundabout Database to find one in your state if you aren’t sure where one is located.
Go to that roundabout, and navigate through it at various times if possible both as a driver and as a cyclist and/or pedestrian (if facilities are provided) and remember how you feel and what you experience.
Then, the next time you are at signal with a red light, either with no vehicles or pedestrians in the area, or if you are 15 cars back from the intersection, think about that roundabout experience. Think about it again also if you are standing at a signalized intersection in pouring rain, wind, or in the frigid cold waiting for the “WALK” signal to let you know when it is safe to cross, or if you are on a bicycle, waiting for the traffic signal to change.
Think about how a roundabout would improve travel for all users in each situation, as well as the overall community experience.
However, it isn’t enough just to be “thinking round.” I’d also urge you to share your experiences with others such as family, friends and neighbors. If you think a roundabout will benefit your community, get in touch with your local and state representatives and see if you can get others to do so as well to advocate for one. Use social media, write letters to the editor in your local newspaper, or perhaps even write an online article such as this one.
Together by “thinking round,” and taking action to get more roundabouts constructed, we can solve many of our current problems and make our roads safer and more resilient, our environment cleaner, and our communities more prosperous and equitable for all.
