The magic roundabout

Based on my experience in driving in Australia and New Zealand, I have written before in favor of ’roundabouts’ (or traffic circles as they are known in the US) as superior to four way stop signs at intersections. But they are not popular here even though there is evidence that they result in fewer accidents.

But I came across this mother of all roundabouts for a very busy intersection in Swindon in the UK that has six feeder roads and seems incredibly complicated but apparently works very well once drivers get used to it. It consists of an outer circle that has five small roundabouts where traffic flows in the expected clockwise direction and a large inner circle where it flows in the opposite direction. (Remember that in the UK they drive on the opposite side to the US.)

In such roundabouts, each peripheral circle facilitates car entries and exits from an associated feeder road. Experienced drivers can traverse the intersection in more direct and efficient ways, saving time. Less proficient motorists may choose to go with the flow, cycling around the edges until they reach their desired exit. For drivers going from one end to the other, a magic roundabout can enable traversals that are up to twice as fast as conventional roundabouts would allow.

The above link provides a gif of what the flow is like for a general magic roundabout but here’s what the traffic flow looks like for the actual Swindon one.

Regulars find it easy to navigate the Swindon magic roundabout but people encountering for the first time may get the heebie-jeebies and fear ending up going around in circles forever, as these two Finns discovered.


  1. says

    A roundabout was installed at a medium-low traffic intersection here in Corvallis, Oregon, and resicence didn’t know how to deal with it and it caused more accidents. A friend lobbied hard to have it successfully removed. Silly fellow Americans.

  2. cartomancer says

    You’d think that a country so used to going round in circles would take to the roundabout very quickly.

  3. jrkrideau says

    I think I was through there as the passenger in the left-front seat of the car.

    I’m familiar with roundabouts. This is a big one but the driver lives in London so I’m not worried.

    Wait a minute! He just reversed directions! OMG!

    A friend of mine who grew up in Hong Kong but learned to drive in Vermont said the first day he was in Paris he got caught in the inner lane of the roundabout at the Arc De Triomphe and just kept going round and round until a policeman hailed him down and drove him to safety.

    I have noticed here in Canada we seem to be turning to more and more roundabouts, everything from a mini-roundabout with some flowers in the middle in residential areas to a 2 or 3 lane one. The local gov’t is planning to install a new one at a major intersection in the next 2 or 3 years. Nothing like that terrifying monster though.

    They do improve traffic flow though anecdotally the larger ones can be difficult for cyclists to navigate and I am a cyclist. I have never had any problem but I have never attempted anything more than two or three lane roundabout in rural France.

  4. fentex says

    I’ve cycled through that roundabout a few times, when I was working in the UK.

    Unfortunately in New Zealand they are gradually disappearing, and I’m not sure why. They are better for traffic flow but for some reason they’re becoming unpopular with the powers that be. It isn’t accidents.

    I know one big one was removed and replaced by lights because it was on the edge of our large central park and it specifically caused problems for pedestrians -- a problem with roundabouts is that traffic at busy ones is ALWAYS flowing, which is a problem for people trying to walk across.

  5. springa73 says

    There are plenty of roundabouts in Massachusetts, but they are called rotaries rather than roundabouts or traffic circles.

    I can definitely see how they can be intimidating to someone who is not used to them, though they flow pretty smoothly when populated by drivers who know how to handle them.

  6. Mano Singham says

    jkrideau @#3,

    I have a vivid memory of when I was a young boy going with my parents to Paris and standing on the outer curb of the circle around the Arc de Triomphe and seeing the non-stop flow of cars going around at high speeds. I have the vague impression that we tried to cross to the center by weaving through the traffic but that must be my imagination because that would have been a sure way of getting killed. I think there is a tunnel that pedestrians use.

  7. jrkrideau says

    @4 fentex
    You must have been mad! Of course my memory of the roundabout is a little vague. Terror seems to have that effect on me.

    It probably would have been fine but I never even though of reverse lane in a roundabout but Peter, the driver, never thought to mention it.

  8. Pierce R. Butler says

    springa73 @ # 5: …There are plenty of roundabouts in Massachusetts… they can be intimidating to someone who is not used to them…

    Two words: Boston drivers. Even on straight flat open roads, these intimidate all others (or at least try their damnedest to do so).

  9. fentex says

    …the circle around the Arc de Triomphe and seeing the non-stop flow of cars going around at high speeds

    I’ve driven around that a few times as well. It’s quite interesting -- I’ve no idea if there’s any rules but people, confronted with such an obvious challenge, seem to have little trouble calming down and working carefully and cooperatively to get through it.

  10. EigenSprocketUK says

    I’ve driven that Swindon magic roundabout. I was expecting it to be odd, but it turned out to be pretty normal. Well, normal for a UK driver who sees a lot of roundabouts.
    Each sub-roundabout does the usual roundabout thing: traffic circulates anticlockwise (because the UK drives on the left). Swindon’s magic roundabout reduces neatly to just a series of normal roundabouts.
    And each roundabout means that at each point you are contending with only the vehicle which is already on the roundabout you wish to enter. This beats a four-way stop sign any day. In fact, I don’t think I’ve ever seen a four-way stop sign in the UK.

  11. EigenSprocketUK says

    Correction to my last comment. We drive round roundabouts clockwise. Oops.(!)
    Anti-clockwise is for European roundabouts where we drive on the right.

    This reminds me that Swindon’s magic roundabout also presents a topologically interesting option. You can go round it anticlockwise (opposite to normal) by driving the correct way round each individual roundabout so that you generally progress in an anti-clockwise manner (e.g. from south-east towards the north). I tried this on my second visit to the Magic Roundabout and did the full 360. It turns out to be surprisingly straightforward, and not at all unsafe because you follow the rules of the road all the way, and at no individual point are you doing anything unexpected which could cause a crash.

  12. EigenSprocketUK says

    @jrkrideau You’re absolutely right: loads of evidence (London Cycling Campaign probably a good source of solid data) that large roundabouts can be really unsafe for cyclists, mainly because of large trucks with poor visibility not seeing bikes on the inside, and motor vehicles having more room to reach higher speeds so that the driver’s focus is on the exit ahead instead of the nearby bike. I doubt this is why traffic lights are becoming common on the largest UK roundabouts, but maybe it’s part of it.
    My anecdotal experience is that UK drivers often misremember the rules of their roundabouts, and are often defaulting to a weird “priorité à droite” which comes close, but leads to poor flow and accidents. The incompetent result is “if there’s someone waiting to my right, then I give way, otherwise pedal to the metal” – a bit like a US 4-way gone badly wrong.

  13. lanir says

    There’s one near me that I use on a semi-regular basis. It’s a two-laner and I find myself having significant disagreements with that design decision. I’m fine with one lane but two or more depend on other people not being idiots AND clearly communicating. The latter has never happened in my experience although I’ve been using the thing for a couple years and the former… Well, it’s certainly not a safe bet. Fortunately I enter and exit in the same locations most of the other traffic does so about 2 miles (in city traffic) before the roundabout comes up I get into the right lane no matter how slow or backed up it is. Then I can avoid using the inner lane and crossing the outer one while coming and going.

  14. Onamission5 says

    My very first encounter with a roundabout was as a teen who’d just moved to a new town, walking home at night, and coming upon a car perched in the center of one, lights on, door open, no occupants.

    The city where I live now recently, within the past few years, installed a simple one to assist with traffic flow at a former 2-stop intersection. It has helped with flow off the side streets considerably-- people coming from either of those roads used to get stuck for quite some time waiting for a break in cross traffic, and now they have same access as the main street. My only (well, primary) complaint is with drivers who seem to believe that they cannot enter the roundabout until all other vehicles have exited, and/or that no other cars are allowed into the roundabout until they are through using it. One would think that people would become accustomed over time, especially considering it’s not the only one in town, but that does not seem to be the case for some drivers. In either location.

    My other complaint is that some folks seem to think this roundabout in particular is supposed to be used for turning doughnuts. There’s a fresh bumper in the median and skid marks on the pavement about once a week, give or take.

    I’ve not had the opportunity to encounter a multi lane traffic circle. If I’m honest, they do seem scary!

  15. EigenSprocketUK says

    For those not of a nervous disposition – here’s a drunk driver who vaulted a roundabout at speed and was lucky to have survived with almost no injuries. As was every other road user at the time.
    BBC News 10 April 2017

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