Commuting 101: Roundabouts

In The Art of War, Sun Tzu advises you to “know your enemy.” I’m not saying that motorists are a cyclist’s enemy (though some of you would disagree,) but I am saying it helps to think like a motorist at times. Back in 2000 a group of researchers studied how motorists interact with cyclists at roundabouts in Finland, Sweden and Denmark. The study used a “stunt cyclist” and hidden cameras to see how drivers reacted to a cyclists presence. I found the study pretty fascinating and you can read the whole thing HERE.

OP Roundabout

“The most frequent bicycle accident type at roundabouts has been shown to be between the entering driver and the circulating cyclist.” That has been my experience. I used to ride a route that included the roundabout pictured above and it was always an adventure. I pulled up and if there was any traffic coming around the circle my way I would just wait until it was clear. The danger now became inattentive drivers pulling up for their turn, who could be looking right at you and not see you…

I’ve had a few discussions with my brother about this and he has given me his unbiased, expert opinion: if there is a crosswalk available, use it. Let me back track a moment and say that my brother is a former bureau chief for the Kansas Department of Transportation and was kinda the guy who brought roundabouts to the state. He has done a ton of research and is now the engineer that other traffic engineers in the U.S. call on for his expertise on roundabout design. So, I’m not kidding when I say that his is indeed an expert opinion.

He says that when bicyclists share lanes with motorists at a roundabout, they have been proven to be injured at a rate of two to three times greater than at a signalized intersection. He reminds me that the percentage of bicycle accidents are VERY small so an increase of 2 to 3 times is still a small fraction…

Still, he worries about me you see. He did say that roundabouts do slow traffic significantly, which is good in the event of a collision.

Another study states that:

“the difference in speed between cars and bicycles at a conflict point is very important: a reduction in collision speed from 30 mph (48 km/h) to 20 mph (32 km/h) means that the risk of fatal injury is reduced from 45% to 15 or 5% (a factor of 3 or 9).”

The study goes on to say

“The speed through roundabouts is determined by the vehicle path curvature. On single-lane roundabouts, an increase in the vehicle path curvature results in a reduction of vehicular accident exhibits. On multilane roundabouts, however, increasing the vehicle path curvature can result in a higher potential for sideswipe collisions. On double-lane roundabouts, designers are faced with a dilemma: accepting a higher number of sideswipe collisions involving motorized traffic (when they increase vehicle path curvature) or accepting serious accidents involving pedestrians and cyclists (when they decrease
vehicle path curvature).”

So, be aware; your risk of being sideswiped increases when you enter a roundabout. If it is a busy one, and I know this goes against the grain, you may want to heed my brother’s advice and hop off the bike and use the crosswalk … carefully.

Finally, I’ll leave you with some quotes from the Kansas Roundabout Guide:

A bicyclist has a number of options at a roundabout, and your choice will depend on your degree of comfort and experience level with riding in traffic. You can choose to either circulate as a vehicle or use the sidewalk around the roundabout. When circulating as a vehicle, be sure to ride near the middle of the lane so that drivers can see you and will not attempt to pass you.


Well-designed, low-speed, single-lane roundabouts should not present much difficulty to bicyclists. On the approach to the entry, signal your intentions and merge into traffic. It is generally safest for bicyclists to claim the lane. Keep in mind that drivers should be traveling at about 15 to 20 mph [25 to 32 km/h]-close to the speed you ride your bicycle. Most roundabouts will give you three options:

1. Ride like a car: If you are comfortable riding in traffic, ride on the circulatory roadway of the roundabout like a car. Obey all of the same driving instructions as for cars. Watch out for vehicles crossing your path to leave or join the roundabout. Watch out for large vehicles on the roundabout, as they need more space to maneuver.

2. Walk like a pedestrian: If you are uncomfortable riding in traffic and no special separate facility is provided, dismount and exit the approach lane before the splitter island on the approach, and move to the sidewalk. Once on the sidewalk, walk your bicycle like a pedestrian.

3. Use a shared bicycle-pedestrian path: Some roundabouts may have a ramp that leads to a widened sidewalk or a shared bicycle-pedestrian path that runs around the perimeter of the roundabout. Be courteous to pedestrians and yield to them.

I might add to #3 that if there is a bike path at the roundabout, make sure you are riding in the direction of traffic rather than the oposite direction (see the first study mentioned for details).

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0 thoughts on “Commuting 101: Roundabouts”

  1. BSR says:

    As a motorist some of the time, I’m a big fan of roundabouts, done properly. Roundabouts are a great idea for cars, but I don’t believe many have been designed with bicycles in mind. The best working ones can process far more traffic in a shorter time than a similar-sized intersection.

    Having driven quite a bit in Europe, my opinion is that most American roundabouts are poorly designed….most of them are too small.

    Part of the problem seems to be the attempt to cram a roundabout into the space formerly occupied by an intersection (so they don’t have to deal with claiming more land, I guess). It’s not so bad, when it’s a single-lane — pretty easy for most motorists to figure it out.

    Where I’ve seen many near-accidents is multi-lane roundabouts in a very tight space, with little or no signage BEFORE you get to it, so that people can plan their routes. If you’re trying to figure out where to go while you’re trying to figure out how this thing works, the result is often near-misses, sudden stops, or just complete vapor-lock while the hapless motorist’s brain tries to catch up. I’m now seeing these a lot in newly developed shopping areas and neighborhoods in the US. Some of them are double-lane for no clear reason — they don’t process enough traffic to warrant the additional complexity.

    The roundabout in your picture appears to be one of the better-designed larger ones, but could still use better signage indicating which roads exit at each point. Some of the signs before entering roundabouts in Europe are HUGE to get all the names in, but they let you figure out where to go before you get into the thing. Then you can concentrate on watching other motorists.

    As far as biking roundabouts — I’ve given up on some of them, resorting to routes that take me around, or (rather than wait for 10 minutes for a clear shot) just take the first exit, double back, and do it again until I’m on the road I need. Not optimal, but it feels safer that way sometimes. Where I live now (Denver) there are none on my regular routes, so I don’t have to deal with them on a regular basis.

    Funniest moment I remember with roundabouts was about 20 years ago I was driving in the UK for the first time (left side) and was trying to drop a rental car off at Glasgow airport. We went through about 4 roundabouts in quick succession, but on the last one, we couldn’t find the right exit and ended circling one about 4 times. By the 3rd go-round, I was laughing so hard I could barely see! Fortunately there wasn’t much traffic right then!

  2. BSR says:

    I’ll add one other observation: Most American motorists don’t know how to deal with multi-lane roundabouts. They don’t seem to understand which lane to get into for the proper exit, and the size of some roundabouts don’t allow lane-changes easily. So you get sudden exits from the inside lane, and such.

    If I remember correctly, roundabouts weren’t taught in drivers ed when I was a kid (it’s been a while) — does anyone know if it’s covered now?

  3. Warren T says:

    Hehehe. Reminded me of this: Hey, look kids, Big Ben … Parliment.

  4. Quinn says:

    I was reminded the other day (thanks to a Caddy running over my cargo trailer) that, here in Reno, bicycles are Motor Vehicles, not exceptions, turn lanes, round-a-bouts, DWIs and all, even if your towing a trailor with your heavy rig, and there is a lifted SUV, with a driver having a Roid Rage behindyou at a light, in fact the traffic cops get pissy when I cyclist stands up for himself,
    so stick to the laws and hopefully you won’t get run over and or in trouble with the law.

  5. Robert says:

    I like round abouts. DePere, WI just finished a major bridge project and added a three lane round about and even gave lectures to the public and the police offered to ride with older folks to teach them how to navigate the round about. The very interesting thing is that the city had the forsight to incorporate a bike lane into the round about and across the bridge. The previous bridge did not have these considerations for cyclists. In fact the old bridege can only ride on right hand sidewalk and walk near pedestrians. Much improvement.

  6. Steve says:

    I have to concur with BSR; roundabouts are a great feature, but depend on drivers being able to successfully navigate them. In the UK they are so common everyone is used to them, and roundabouts of roundabouts are seen fairly regularly (eg, there’s one in High Wycombe I used to cycle round regularly as a teen). In North America they’re so rare most drivers don’t know how to navigate them and panic easily. Here in Halifax the clumsily named Armdale Traffic Circle is a roundabout in all but name, and notorious for the traffic backups because drivers are unable to successfully negotiate and merge once on the circle.

  7. Dave says:

    I currently live in Germany where roundabouts are common. In my experience most Americans are not very good with them and I even find myself (also an American but I pride myself on driving skill) traveling a few miles per hour slower than germans through the multi-lane ones. The other day though as I was circling the roundabout the traffic in front of me began to noticably slow for no apparent reason. I was gratified to see that the driver who was about to exit (and who normally has the right of way) was slowing to allow a cyclist on the sidewalk to cross his lane.

    Here in Germany, take the sidewalk, they have to stop for you, they tend to see you, and it is a safe and efficient way to get through the intersection.

  8. I have to say that it depends on the circumstances as well. Here in DC, there are plenty of roundabouts and bikes, and everyone is pretty much accustomed to both. That doesn’t mean that this, or any, city is safe for bikers–I was run off the road into a parked car on a perfectly straight section of road–but I think that the more common roundabouts and bikers are, the fewer problems there are.

    That said, I do agree with everyone who pointed out that we Americans aren’t very good in roundabouts–either driving or designing them. Here in DC, they do all kinds of wacky things with them, including dropping in dozens of signals, which drives me bonkers, since they usually confuse the issue more than they do facilitate traffic flow.

  9. Bob Giordano says:

    This is helpful, and also reinforces what I’ve been thinking and observing for a few years now: single lane roundabouts work great and are very safe for all modes, while multi-lane roundabouts should be avoided, especially in urban areas.

    Missoula Montana has about 64 signalized intersections. The first 2 roundabouts on arterial roads (both will be single lane roundabouts) will be built in summer 2008. My group is thinking that a system of single lane roundabouts will work best. Yet, in order for the roundabouts to all be single lane, that means the approach legs can only be 2-lane roads, not 4-lane roads.

    A 2-lane road (with either a landscaped center turn lane or periodic left turn pockets at minor intersections) can carry about 22k cars a day. An undivided 4-lane can carry about 26k cars a day. That is with signals. With roundabouts, the 2-lane can carry about 26k a day- the same as the 4-lane with signals! But the 4-lane with signals will have many more _severe_ crashes, stop and go traffic, noise and pollution, and higher land requirements. Pedestrians have been getting killed when one lane stops and a second inside lane does not.

    In the context of a more sustainable transportation system, the 2-lane roads with single lane roundabouts can be coupled with great bus/train service, connected bike lanes and off-road trails, some car sharing and bike stations, and so on. Each city will be different, but I’m working on some of the principles to be put into motion- and soon.

    Please email me at if you have insights, comments, etc. thanks. -Bob Giordano, Missoula Institute for Sustainable Transportation.

  10. Joe G says:

    I came across this after reading about bike fenders and, even though this topic appears to be older than most kindergarteners, I’m compelled to chime in in response to the 2nd comment by BSR above.

    Circular intersections really come in two flavors: One type is the “Big Ben/Parliament” type where you need to be on the outside to exit. This design is common in Spain, Germany, and the Netherlands. In this design, there’s a circle road, and entry and exit is a right-turn movement. You can get trapped in the inside lane, and you can circulate as many times as you like in the outside lane.

    Most roundabouts in the US, however, especially those built in the last 20 years, are different. This design, which is the standard design in the US, Australia, New Zealand, and the UK, does not have a true circle road but only a circular island that separates one-way pairs. In this design, exiting the roundabout is a straight-ahead movement, not a right turn.

    So, back to BSR’s comment: In the US/Aussie/UK design, you are NEVER supposed to change lanes within the roundabout. You ARE supposed to exit from the inside lane. Paths never overlap because the proper lane MUST be chosen before you enter the roundabout: keep left to turn left through the roundabout and exit directly from the left (inner) lane.
    For cyclists, the information presented in this article is sage advice. Take the lane, stay centered, make yourself visible, and be alert for drivers doing dumb things. Use the pedestrian facilities if you like.
    About the worst possible thing anyone could do as a cyclist is to try to ride around the perimeter of the roundabout and past an exit. Doing so in a US/UK/Aussie/NZ design equates to making left turns from the right-hand lane. It’s illegal and very dangerous. (BTW, it is also illegal for drivers to pass an exit in the outside lane).
    A good visual is at Notice how the left lane leads straight out of the roundabout, not around it.
    Overall, roundabouts calm traffic speeds while reducing unnecessary waiting for drivers and cyclists alike. But user confusion remains a problem, as this thread indicates.

  11. Richard Poor says:

    I would like to see the Dept of Trans separate statistics for the practical single lane roundabouts from those of the multilane monstrosities. Everyone seems in agreement that the single lane roundabouts are safer and more efficient than an uncontrolled intersection or a 4-way stop.
    The problems are with the high volume multilane roundabouts being put in place of traffic lights. From the information I am given they cost more to construct, more to maintain, result in more congestion during rush hours, result in more accidents for pedestrians, bicyclists, and cars; result in more property damage, and the one upside is fewer fatalities.
    Wouldn’t we be better off if instead of spending money on the roundabout we used to hire more traffic cops to watch dangerous intersections?

  12. Amanda says:

    We have quite a few single lane roundabouts. I don’t mind them except that they slow the traffic down so much. On some it’s ok, but on some I really have to slow down a lot because the cars have to travel a tighter angle than I do.
    I scared a driver entering a roundabout in front of me the other day by making him think he was going to hit me. I was perfectly safe, but I wanted him to realize he can’t count on cyclists to go as slow as he thinks.
    Honestly, I think that’s usually the problem. Most people think cyclists go about 10 mph which is true uphill, but speeds above 20 or even 30 are not uncommon in some areas. Plus, cars think they go faster than they do. They think about cruising speed but forget about all the slowing they do. A turning motor vehicle is rarely going faster than a cyclist.

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