Roundabout in Anacortes
3-way Roundabout in Anacortes at Commercial Avenue and SR 20. WSDOT Photo.

One of the classic games that I play with my family when I go to France is: where did they put in a new roundabout?

To American drivers, Europe is known for its numerous roundabouts. The invention has revolutionized driving through intersections and has made improvements in all domains, including accidents, gas consumption, the numbers of cars that get through or even pedestrian friendliness.

The invention has yet to come into full force on the other side of the Atlantic and Americans are reluctant to give up their less-efficient 4-way stops and traffic lights. The benefits are numerous though:

  • Roundabouts are part of the solution to America’s traffic violence problem as they reduce accidents by 40% and fatalities by a whooping 90% over 4-way stops or lights.
  • By not having cars idling as they wait their turn in a “traditional” intersection, roundabouts reduce gas consumption by 30% and make for less polluted cities
  • Roundabouts require much less maintenance (versus electrical maintenance in lights) and are much cheaper than any other type of intersections in the long run
  • Roundabouts make street crossing much safer for pedestrians in many ways. First, they split the crossing into two parts, already reducing crossing distance by half. They also eliminate the sometimes numerous turn lanes which can easily double the width of a street. This often leads to crossing distances being a forth shorter than previous intersections.
  • They also make cyclist’s lives easier by making left turns from the right lane possible. Reaching left turn lanes on busy streets often require crossing two lanes of fast-moving traffic, a stressful experience for bikers.
  • They provide more open space in the city, whether that would be used as green space or for public art.

In Seattle, roundabouts would be a welcome sight to streets that have enough capacity for cars to use them but not enough capacity at intersections. They would improve dangerous intersections for all modes of traffic. They are also the only intersection system that works well with 5 (or more)-way feeder roads, which are especially numerous with Seattle’s colliding grids.

5-way roundabout
5-way roundabout at SR 542 and Smith Road, East of Bellingham. The Roundabout’s ability to deal with 5+ way traffic is well captured here. WSDOT photo.

Roundabouts should be located throughout Seattle in various dangerous or congested intersections. Some suggested locations include:

  • Seattle Blvd/5th Ave/Dearborn St in the International District
  • 2nd Ave Ext/3rd Ave/Main St in Pioneer Square
  • Denny Way at:
  • Stewart St/Yale Ave
  • Wall St/Battery St/Aurora Ave/7th Ave
  • Westlake Ave/Nickerson St/Dexter Ave/Fremont St at the south end of the Fremont Bridge
  • Fremont Way/Fremont Ave/39th St
  • The Montlake Triangle
  • Rainier Ave/Hill St/23rd Ave
  • Rainier Ave and MLK Way
  • Marginal Way/Chelan Ave/Delridge St, at the west end of the West Seattle Bridge. This is a major intersection problem on the Alki bike trail.
  • Fauntleroy Way at 35th Ave, Avalon Way and Alaska St
  • California Ave/Edmunds St/Erskine Way
  • All over Madison Street from Broadway to Madison Park

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Guy is a high school student in Bellevue with a strong desire to become an urban planner. Before moving to Bellevue, he grew up in the Paris metropolitan area where he fell in love with and learned from some of the best rail systems in Europe. Translating his experiences from abroad to Seattle, Guy is now passionate about improving this region's public transit (especially marine-based transportation) and cycling infrastructure. Aside from the technical side of things, Guy also enjoys photography and music.

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Scott Bonjukian

As a driver I like roundabouts, but I can’t comment on whether they are preferable for pedestrians. I’m tempted to think they take longer to cross diagonally.

The problem with them is they require much more space than a standard intersection; if the right-of-way isn’t wide enough, building them will typically require easements on private property or condemnation, especially in built-up areas where buildings are at the property line. I would prefer they be built in suburban areas where traffic design dangerously encourages higher speeds.

Stephen Fesler

I share some similar concerns. But there are intersections even in Seattle that they probably could work exceptionally well. And even be a case for making the street skinnier by reducing lanes and turn lanes. We do have some very wide streets.

Scott Bonjukian

Page 20 of this PDF shows some recommendations from the feds.

You’re probably right that we could go reasonably smaller, especially if building these in conjunction with road diets. 15th and Campus Parkway in the U-District comes to mind as a place that could use some traffic calming and has space.

Matt the Engineer

Nice. Page 128 is what interests me. Maximum radius to keep cars under 15 mph = 40′. I just measured a residential traffic circle and they’re around 27.

Scott Bonjukian

Is that the width of the center island or the outside diameter of the entire circle? I guess I’m confused about that for the PDF I linked to too, where it says “inscribed” circle, which I assume means the entire circle.

Matt the Engineer

P. 131 has a labeled diagram. The inscribed circle appears to be the largest circle you can draw without hitting the outside curb.

Stephen Fesler

I have but one caveat: the design of roundabouts. You want to ensure that there are short, safe crossing points for pedestrians and that cars will adequately stop for them. The more a roundabout forces speeds to slow (let’s say below 20mph), the safer they are for peds and cyclists. You don’t want multi-lane roundabouts because of width and increased ability for speed and lack of yielding. The smaller the turning radius for vehicles and increased chokers leading up the roundabout, the better. I can think of cases of miserable roundabouts, which were horrifically designed in Cork City.

Bad Case Examples
Kinsale Road:,-8.470111,3a,75y,344.62h,74.8t/data=!3m4!1e1!3m2!1sucBQ8ZBspX6ec1Y5jYS18g!2e0

Positive Case Examples

Matt the Engineer

I completely agree. I think the fundamental criteria to focus on is roundabout diameter. The ones in the pictures above allow for probably a good 30mph. That’s unacceptable at an intersection in a city. Having a very small diameter intersection requires a slower speed.
Although it’s tough to imagine big roads funneling down to a little residential-size roundabout, I can’t think of a reason not to do it. It’s faster for cars than a stop sign, but safer for pedestrians.


Yeah, I think it depends on the road. For example, I can’t imagine Aurora or Lake City Way funneling down to one lane so that folks can travel in a roundabout (even though, as you said, it might lead to higher throughput). But Fremont or Greenlake? Oh yeah. No one likes those intersections. Not the pedestrians, not the cars, no one. A roundabout would involve only minor merging (less than half the streets) but pretty soon even the most hard core bike hating, pedestrian hating driver would admit that it is an improvement.


I agree, I think multi-lane roundabouts are kind of crazy. I forgot they had them. The only one I know about around here is in Olympia, here:
Not only are they bad for pedestrians (arguably forcing the need for pedestrian overpasses, which are a problem in their own right) but they are bad for drivers. I’m sure the locals get used to it, and figure it out. But in a country where simple roundabouts are rare, multi-lane roundabouts must cause a lot of confusion (and accidents, or near accidents). It doesn’t help that the direction sign looks like the symbol for the artist formerly known as Prince ( Confusion leads to less efficiency. All of that means that the gain you get in car throughput from a multi-lane roundabout compared to a traffic light is probably a lot less than the difference between a single lane roundabout and a traffic light.

In the case of that one in Olympia, they really didn’t gain much by having it be multi-lane. There are still the same number of lanes going around the roundabout (one). The only benefit is that those that are turning right don’t have to enter the roundabout. That is OK for those that turn right onto a two lane street, but in this case, not everyone does. For almost every situation, this means the driver has to yield to someone in the roundabout anyway.

I think in this case, in every case really, they should just funnel people into one lane, then lead them into the roundabout, then allow for multi-lanes again. Or, if they really need two lanes of traffic going at all time, they should stick with the traffic light. In many cases in Seattle, such as some of the examples I mentioned, the road widens to two lanes mainly because of turn lanes. For example, North 39th Ave. is one lane each way most of the time, but widens to two lanes (eastbound) right before Fremont Avenue. Replace the intersection with a roundabout and you wouldn’t need the extra lane. If I’m not mistaken, the only street in that five way intersection that allows for two lanes to go straight is southbound Fremont Avenue. Making that one lane would not be much of a loss, since most folks in that lane are turning right, and the two lanes converges to one lane and one parking lane right after the light.

Matt the Engineer

The one piece I disagree about is efficiency. That equals speed. Believe it or not, it’s actually a positive thing to create confusion on the roadway. Confused drivers slow down.

Stephen Fesler

What I meant by efficiency is this: Pedestrians don’t have wait for a walk man to say “walk”, and neither do cyclists and drivers. That’s efficient whereas everyone loses at a stoplight. A simple 4-way stop is likely to be a different matter. Although, many can still be miserable like 5th Ave and Banner Way. Death zone for pedestrians–not that they have much reason to walk there anyway. But my point wasn’t about more efficient *high speeds* which stop lights do encourage.


I agree Stephen. Efficiency often means avoiding zero. It is the old tortoise versus hare thing. If you can avoid spending time going nowhere, you are way ahead of the game (in the city). This is counter intuitive, especially if you are used to traveling between cities. If you are driving from Seattle to San Diego, then absolutely, going 70 versus 65 makes a big difference. But if you are going from Northgate to downtown — absolutely not. If you are going from Ballard to the UW, there is simply no way you are going to 70 MPH anyway (unless it is late at night and you are running for city council). You are lucky if you average 30 MPH (very lucky). That is why they deliver important, time sensitive documents via bicycle. Of course a car, any car, has a higher top speed But a bike rider can avoid time spent going nowhere, which is why he (or she) can get the papers there sooner. So, yes, that is why roundabouts are more efficient. It isn’t that cars go faster through the intersection (quite the opposite) — it is that cars rarely go zero. There is no waste. If you are waiting then you are waiting while another car goes through (which is way more than you can say about a typical intersection).

But back to confusion. Sorry, Matt, I have to disagree. Confusion is not good. A confused driver is a dangerous driver. A confused driver might slow down; might even come to a complete stop, but someone else (maybe an experienced driver who is tired, impatient, and just wants to go home from a hard day at work) won’t wait for the confused driver. He will drive around the other driver, and not look for pedestrians (especially if they are rare). Meanwhile, the pedestrian, who may have timed the entire process just right, didn’t count on the one driver stopping, and the other driver changing lanes, and next thing you know, you have a mess on your hands. Confusing intersections are deadly intersections, ask any biker (biker as in bicyclist, or biker as in motorcyclist).

If people drive too fast, then add speed bumps. Or, if it is unmarked intersection, add traffic circles. Or put the road on a diet (three lanes instead of four). Nothing confusing about that in the least, but they do a good job of reducing speed (and accidents). That is a lot different than a two lane traffic circle.

Stephen Fesler

FYI, I don’t know why actual Google Maps are showing. I meant for people to view the Street View links.


I do a lot of hiking, so I’ve noticed a lot of new roundabouts in the areas surrounding Seattle. They seem to work just fine, and seem to work better over time (as people get used to them). I’m surprised that they work better for pedestrians (versus traffic lights or even stop signs). If traffic isn’t very heavy, I’m sure they are great for people walking. But if traffic is heavy, it seems like people are concentrating on the other cars, and wouldn’t notice a pedestrian. Specifically, people are looking to the left to see if someone is in the circle and going to stay in it. It is almost like everyone is taking a “free right” all the time, which as any pedestrian knows, is a very dangerous situation. Maybe I’m missing something (like maybe the pedestrian walkways are around the circle a bit so that only cars already in the circle have to stop).

I think the best place for roundabouts in Seattle are the five way intersections. One example is at 50th and Stone Way. At first glance, it looks like a roundabout might not work — since there are two lane roads heading there. But with one exception (northbound Stone Way) none of the streets allow two lanes to just keep going straight. They all branch off, with one lane being forced to turn. So, basically you would force all of the streets to first merge into one lane, then go through the roundabout. This means a little less room for the cars (since part of one lane will go away) but that is a very small price to pay for what would undoubtedly be faster throughput. Five way intersections are terrible which explains why it takes forever to go through that intersection, even when there aren’t that many cars there.

The Fremont Way/Fremont Ave/39th St is very similar, as are various intersections on Madison and Nickerson. They are all the result of the having a diagonal street in the middle of a grid.


SDOT should model 50th & Stone Way.

Matt the Engineer

Seattle was a pioneer in traffic circles, and installed our first ones in 1973. At the time of this report in 1997 there were 600 of them in Seattle. My Queen Anne neighborhood is full of traffic circles and I love them.

Here’s the process to request a new traffic circle.


I think most of those traffic circles replace unmarked intersections. These are very good. But how many circles (or roundabouts) in Seattle replace four way stops or traffic lights? My guess is not that many.