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Magic Roundabout (wikipedia.org)
37 points by subsystem on Dec 13, 2012 | hide | past | favorite | 44 comments

As a child, I lived in England for a brief stint (around a year) because my dad was transferred to his company's British branch. We lived somewhere near the Magic Roundabout (Bovingdon, which I think is pretty close).

We had just moved, so both of my parents were still getting used to driving on the opposite side of the road. And roundabouts in general. I have fond memories of my mom getting stuck on the Magic Roundabout for about an hour, too terrified to leave. So we just kept going round and round and round. Being a small child (3 or 4 years old), I just kept telling her every-time we passed the same building.

"Mommy! There's that building again!".

I'm sure she wanted to reach back and strangle me. When she eventually mustered the courage to exit...she did something wrong and we stopped up the whole roundabout. I don't actually remember that part, but she claims traffic basically ground to a halt until she maneuvered her car out of traffic.

Fond memories =)

Edit: Based on another commenter, looks like it was the "Plough" roundabout, not the one in this article. Whoops!

This is basically two normal roundabouts, one inside the other, with traffic direction the opposite way in the inner lane. Or a two-lane roundabout. It allows you to spend less time on the roundabout if you want to take the junction to your right, as you would usually have to go to your left and do an almost complete lap.

Compare reaching your parent on a singly-linked list to a doubly-linked list. Being able to traverse in either direction may provide significant performance boosts...

Going by the diagram, I think it makes more sense to think of it as 6 roundabouts in a circle. The inner "reverse roundabout" is just you entering and leaving each roundabout by the first exit in turn. The "outer roundabout" is similarly you entering and leaving via the second exit of each roundabout. Neither of those is a true roundabout as you don't have right of way once you're on it.

In terms of driving, the five-roundabout perspective makes more sense (for reasons of right-of-way, as you say). In terms of algorithmic complexity, if we are considering distance traveled by the average vehicle, the two-nested-roundabouts perspective makes more sense.

Incidentally, most of the traffic comes from Queen's Drive, Drove Road, and Fleming Way (Shrivenham road has been closed to through traffic for many years). Having ridden across it on a bicycle regularly as a teenager, it works surprisingly well.

Yes, it's just a circular road which happens to have lots of roundabouts on it.

I used to live close to this one: http://en.wikipedia.org/wiki/Magic_Roundabout_(Colchester) - it's actually very easy to do, and is really nothing more than a road that happens to run in a loop and has 5 small roundabouts on it. The junction in the current configuration works a lot better than it did when it was a large regular roundabout, as the pattern of traffic made it almost completely impossible to enter the roundabout at some of the entrances.

That's the one I'm near too. It isn't actually that hard. You just need to treat it as a normal road and not a big roundabout.

After studying it for a bit it isn't too difficult to figure out how it works, and I'm sure if you drove through it every day it would even become boring, but if I encountered this roundabout blind without knowing anything about it I'd probably cause some sort of accident.

Most people slow down.

Slowing down means more time for observation and reaction. As a result, it's actually quite a safe interchange.

(Most traffic accidents are the result of inattention coupled with insufficient reaction time. If you aren't paying attention, bad things happen. If you are paying attention but there isn't enough time to do anything about it, bad things happen. Thus, safety is highly correlated with both getting driver attention and increasing the time available for reacting.

Narrow twisty mountain roads are often much safer than the country roads leading up to them -- because drivers know they need to be involved and aware. Long straight highways are safe at high speeds because drivers can see obstructions and changes far in advance.

I wonder if the 5/4 meter of the XTC song "English Roundabout" http://www.youtube.com/watch?v=akrD84P_zxU (they're from Swindon and the Wikipedia page mentions that the song is a tribute) is a reference to the 5 external roundabouts.

I have been there once. It was the scariest roundabout I have traversed. The contra rotating flow (inside goes one way, outside goes the other) makes it extra exciting.

Myself too. Hangar Lane is far scarier as the driving mentality is central London style and there are 7 lanes.

Hanger Lane is scary as most drivers haven't realised that it's not really a (proper) roundabout any more.

On a normal roundabout if you stay in a lane (one of the inside ones at least) you'll just keep going round and round.

With the redesigned Hanger Lane you get in the lane marked for your exit and the outer lanes slowly peel off as feeders for the appropriate turnings. If you want to keep going round and round you'll need to keep moving over to the right (since we go round them clockwise) every so often to keep from being directed off eventually from your current lane.

[EDIT] It's a "Spiral Roundabout".

That's how you're supposed to do it. Here's how it ends up on a Saturday afternoon:

You queue for 30 minutes on the A406 with 9000 people who have left Wembley Ikea bashing your head on the steering wheel, then sling your car onto Hangar Lane like a trebuchet the moment the opposing traffic lights have gone red (not yours have gone green), slide across three to five lanes randomly, swerve to avoid the Polish truck driver who can't see you because his vehicle is LHD, avoid the police car parked on the inside to protect the previously crashed vehicle, shout "fuck you" out of the window a few times at other drivers, the traffic lights which have screwed you repetitively and any pedestrian zombies trying to short cut it across the junction and possibly several people trying to clean your windows, middle finger the BMW on your left which wasn't there two seconds ago, then desperately try to force everyone out of your way honking wildly as the 2 lanes onto the A40 narrow to one...

Followed by speed up/slow down for a bit because of the Gatsos then a celebratory victory McDonalds (and to shut the kids up) at the A312 junction a few miles down the road (or American Diner on the A40 if you want to spend the entire evening on the toilet).

I don't know about the UK, but in the other countries I've been to, the default roundabout is as you described. The "spokes" of the roundabout (the exits) are narrower than the roundabout, and only the outermost circle of the roundabout traffic can "peel off" into the exit. To keep from leaving at this turn, you need to go in towards the center, then make your way back out at the turn you wish to take.

Isn't every big roundabout the same? I drive via Old Street roundabout in London almost every day and it certainly is spiraling. When I took my driving lessons a year ago, my instructor was saying this configuration is pretty normal.

not really, being from the US and now living in the UK, the "traffic circles" I've gone round in the US were really just circular roads with one lane of traffic and easy to get stuck on if it's busy and you stray too far to the center. Quite different from UK roundabouts.

Not saying all US traffic circles are like that of course.

I hear you. Although that roundabout is scary, some of the entry ramps to the A-14 are worse. It feels like you have 3 meters to merge with two lanes full of inexpertly driven lorries.

Ha I know the ones. The worst one is coming out of the Fenstanton junction towards Cambridge. Did that in thick fog and the dark a couple of days ago.

I know the place! Give me that roundabout any day. At least that way everyone is scared into being careful.

Only the clever people are scared into being careful :)

Raleigh, NC installed a two-lane roundabout a couple years ago[1]. Drivers could not handle it[2] (almost daily crashes) and it had to be reduced to a single-lane roundabout[3]. I can't imagine what Raleigh drivers would do faced with the Magic Roundabout.

1. http://www2.acs.ncsu.edu/trans/planning/construction/Brochur...

2. http://www.raleighpublicrecord.org/news/2011/09/12/accident-...

3. http://www.newsobserver.com/2012/07/25/2218567/crash-prone-r...

There's been a bit of a roundabout fad in the Triangle area, actually. They installed a couple in Wake Forest (a nearby town), and there's actually three near the spot you mentioned now. As a British expat, I am personally fine with them, but people around here do tend to have issues with them.

The upshot of this is that one of the most terrifying things I've done recently was to try to navigate all three of the roundabouts, in succession, on a bicycle, at the same time as two or three buses.

>> Raleigh, NC installed a two-lane roundabout a couple years ago[1].

Interesting, 2-lane roundabouts are very common here (Netherlands), but I don't find them much more difficult than single-lane roundabouts. That Magic Roundabout on the other hand looks insane :-S.

Gotta wonder how drivers from Raleigh, NC would like the 'roundabout' around the Arc de Triomphe in Paris though ;-)

being from Swindon, I'm very proud to see this on the frontpage of hacker news! I took my driving test on it...

It's actually a lot easier to navigate than it looks, you can essentially treat the whole thing as one giant roundabout by taking the second exit on each mini-roundabout.

I too took my driving test on this beast. I spent a good part of a driving lesson learning the different routes across it.

If you consider that I'm from the part of the world where everybody is driving on the right side (see what I did there?:) of the road, it was not a complete disaster. Up and close this magic roundabout actually is not so magic - just one large roundabout with few smaller entry/exit roundabouts. Though, first timers could easily drive round and round for a while.

The UK is not exactly alone in driving on the left : Nations like Japan, India and Indonesia keep it company (among the 76 [0])...

One explanation that always made sense to me is that when driving a manual/stick-shift car, taking your dominant hand (statistically the right hand) off the steering wheel for a secondary task like changing gear is more dangerous... YMMV

[0] http://en.wikipedia.org/wiki/Right-_and_left-hand_traffic#Ju...

Yes, I'm informed. This comment was not ment to be insulting to those who drive on the wro.. left side of the road. Just an observation of specific roundabout from a person, who drives on right one each day.

That might indeed make drive/sit-on-the-left better -- but I think it's not where it originated from, the drive-on right/left distinction has existed since the days of horse and carriage, before there were gear shifts or steering wheels!

Although apparently the origins DO have to do with keeping your dominant hand free for various tasks!


Also Australia & NZ. Most people forget those two.

>> I'm from the part of the world where everybody is driving on the right side

and all because of one Napoleon ;-)

I speak in jest. I know the story is apocryphal, but I am not going to pass the opportunity up - aka let facts get in the way of a good story [-;)

I went round a similar system first thing on Tuesday morning, the Plough roundabout in Hemel Hempstead:


Driving through was surprisingly easy (not to mention efficient), especially given how chaotic morning rush-hour driving can be.

When I was learning to drive (in Hemel Hempstead), I found it easier to get around the magic roundabout if you just thought about it as a road that happened to be a small circle with a few mini-roundabouts on it. Even when it's busy, I've found it quite straightforward to get around, mainly because you rarely have to wait long at a mini-roundabout (if the car to your left is turning right, you can start going since the car on the right is blocked).

Similarly interesting/confusing is the Traffic Light Tree that was in Canary Wharf, London. It's recently been removed to make way for some roadworks.


Note that it's art rather than something functional.

We have a similar roundabout in Colchester where your driving instructor would take you if you were being cocky. It is actually incredibly easy to use if you treat it as a load of mini roundabouts.

It's funny how this ended up on here - this article about "nail houses" was recently posted today: http://news.ycombinator.com/item?id=4915398

The magic roundabout is mentioned in another posting on that same site: http://www.theworldgeography.com/2011/08/top-10-strange-stre...

We must go deeper. But seriously, are they all that rare? There's one similar just down the road from me (Colchester) and it's a pain when you're learning to drive.

I've been through this once. It was terrifying, and I wasn't even driving. It's a good system, but frightening to behold.

I'm curious how one of google's self driving cars would fare on this.

Isn't there another one of these in Essex somewhere, other than Colchester? I seem to remember passing it on the way to Canvey.

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