
Magic Roundabout: Circumnavigating the World’s Most Complex Intersection - misnamed
http://99percentinvisible.org/article/magic-roundabout-circumnavigating-worlds-complex-intersection/
======
ChuckMcM
As a systems guy I love roundabouts. They make it so much easier to get across
intersections and they completely eliminate the variable cost of left hand
(right hand if you're British) turns. That is because traversing them and
exiting simply a linear function of traffic and not based on whether or not
there is a special light for cross traffic turns which may or may not be timed
appropriately. Thus it is always the "fastest" way to get from point A to
point B by travelling along the highest flow routes.

That differs in the US where travelling a slower, but less controlled side
street can be faster than using boulevards with left turn lights.

~~~
david-given
Roundabouts are awesome --- self-organising, self-managing, power-free traffic
junctions! But they do have a failure mode, which is that they tend to starve
low-traffic loads if the traffic is too asymmetric.

For example: consider a T-junction with a roundabout at the junction. (Very
common in the UK.) Most of the traffic is travelling across the T in a
straight line. But I'm entering the junction via the cross road.

The rules are that traffic from the driver side has priority over me, but that
I have priority over traffic on the passenger side. So I stop at the line and
wait for a gap.

With balanced traffic, I'll be guaranteed a gap because the oncoming traffic
will have to stop to wait for someone else, which means I can move onto the
roundabout ahead of the vehicle they're waiting for. But with unbalanced
traffic, there won't be a gap, and I'll be stuck.

Typically what the traffic planners do at this point is add traffic lights,
which is basically giving up, and defeats the whole point of having a
roundabout in the first place.

...I used to live near this monstrosity, which had lights at every stop line.
Blech.
[https://www.google.co.uk/maps/@51.436168,-0.8971696,200m/dat...](https://www.google.co.uk/maps/@51.436168,-0.8971696,200m/data=!3m1!1e3)

~~~
viperscape
West Palm beach, fl had large round abouts installed about 10y ago and I
thought that was great, except with little traffic at the time it seemed
wasteful in time navigating and more importantly in space. I think the idea is
great though, it's safe and usually gives everyone a fair shot to get moving
without much delay.. I'd be interested in knowing how the diameter of the
round about is decided on, specifically is it some algorithm based on
predicted traffic congestion numbers.

~~~
viperscape
If you're curious:
[https://goo.gl/maps/so6EDBad15K2](https://goo.gl/maps/so6EDBad15K2)

~~~
spc476
South Florida has quite a few round-a-abouts. There's a few in Hollywood and
Lake Worth as well.

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julian_t
Ah yes, the Magic Roundabout... indelibly written in my memory, as my first
encounter with it was on a freezing January morning in thick fog. I had no
idea what on earth was going on.

The one at Hatton Cross is pretty good as well
([https://www.google.co.uk/maps/@51.4679146,-0.4230654,172m/da...](https://www.google.co.uk/maps/@51.4679146,-0.4230654,172m/data=!3m1!1e3))
especially since a traveller may come across it, jet-lagged, and having just
picked up a hire car...

~~~
christoph
There's one close to me as well - not as complicated to drive on as you would
think looking at it from the top -
[https://www.google.co.uk/maps/place/Hemel+Hempstead,+Hertfor...](https://www.google.co.uk/maps/place/Hemel+Hempstead,+Hertfordshire/@51.7464173,-0.473929,185m/data=!3m1!1e3!4m5!3m4!1s0x487640d05cd71ac1:0xf0e07f1fcfdff2b2!8m2!3d51.753241!4d-0.448632)

~~~
DonaldFisk
I've been on the one in Hemel on my bicycle. There's also one in Colchester:
[https://en.wikipedia.org/wiki/Magic_Roundabout_%28Colchester...](https://en.wikipedia.org/wiki/Magic_Roundabout_%28Colchester%29)

In addition to magic roundabouts, Britain also has gyratory systems, which are
like normal roundabouts, except much larger and possibly with buildings in the
centre, reachable on foot via underpasses (which are called subways in
England, just to confuse Glaswegians and New Yorkers). The most famous one is
at Hanger Lane in London, which has a tube station in the middle.

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trentmb
As an American, I honestly think I'd just put my car in park and sob
uncontrollably if I came across this.

~~~
SOLAR_FIELDS
We are currently experimenting with other strange interchange designs in
America. I present to you the diverging diamond:

[https://en.wikipedia.org/wiki/Diverging_diamond_interchange](https://en.wikipedia.org/wiki/Diverging_diamond_interchange)

We have one near where I live that opened a few months ago. There appears to
be an adjustment period for our drivers. I have spoken to people who drive the
diverging diamond near us on a daily basis and they say at least once a week a
motorist who is not used to switching from the right to the left hand side of
the road goes the wrong way, risking a head-on collision with oncoming
traffic.

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grecy
I'm from Australia, and have been living in Canada/USA for 10 years.

Yesterday I flew to the UK, and drove around with a friend today. Immediately
one of the first things I noticed and commented on was how much better traffic
flows. We hardly stopped, and just kept moving through roundabouts.

Is there any world where four way stops make sense?

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mabbo
My manager insisted we should rent a car and just drive everywhere on our work
trip to the UK. As the cab entered one of these monstrosities, he turned to me
and said "you know, maybe you were right and it's best we didn't try this
ourselves".

Still, it seems very efficient...

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anoother
Huh, I didn't know these were a) a 'thing' (as in, more than one across the
UK, and b) officially called 'magic roundabouts'.

I've encountered one in Hemel Hempstead; it was a little scary (istr you can
see traffic coming 'towards' you), but the article makes me want to go back
and try it out again.

Edited to add: Between this and the horrific Welwyn Garden City one-way
system, I guess Hertforshire must have (or have had) some of the maddest
traffic planners in the UK...

~~~
ZenoArrow
I think Birmingham may have Hertfordshire beat, particularly with the infamous
spaghetti junction...

[http://www.telegraph.co.uk/motoring/news/6662562/Birminghams...](http://www.telegraph.co.uk/motoring/news/6662562/Birminghams-
Spaghetti-Junction-Britains-most-intimidating-road.html)

[https://en.m.wikipedia.org/wiki/Gravelly_Hill_Interchange](https://en.m.wikipedia.org/wiki/Gravelly_Hill_Interchange)

~~~
russell
From your second link: >>>The junction provides access to and from the A38
(Tyburn Road), A38(M) (Aston Expressway), the A5127 (Lichfield Road/Gravelly
Hill), and several unclassified local roads. It covers 30 acres (12 ha),
serves 18 routes and includes 4 km (2.5 mi) of slip roads, but only 1 km (0.6
mi) of the M6 itself. Across 5 different levels, it has 559 concrete columns,
reaching up to 24.4 m (80 ft). The engineers had to elevate 21.7 km (13.5 mi)
of motorway to accommodate two railway lines, three canals, and two rivers.

Truly an inspiration to those of us who grew up with Erector Sets and Tinker
Toys.

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nateberkopec
FTA:

> and has been adapted to create other ring junctions around Britain:

That's a GIF recording of Cities: Skylines, not a roundabout in Britain.
Purple pollution in the upper-right gives it away.

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yardie
I've traversed it and it's not that bad. Google Maps on an iPhone is horribly
useless in roundabouts (I've mentioned it on HN a few times). Apple Maps is a
little better. I found our 6 year old TomTom to be the best at giving
directions. Having a bit of spacial awareness helps a great deal.

~~~
SOLAR_FIELDS
It would make sense that the Apple version would be at least fairly reasonable
with roundabouts then; as they currently get at least a portion of their data
from TomTom.

~~~
yardie
Apple seems to rely on a mixed bag of suppliers that are not Google for their
map data. I'm not surprised it's TomTom and that may be why it's gotten so
much better after release.

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vermontdevil
In the US, Carmel, Indiana has the most roundabouts. They just installed over
100 with many more on the way.

Ironic as the first automated traffic light was also installed in Carmel.

[http://www.carmel.in.gov/index.aspx?page=123](http://www.carmel.in.gov/index.aspx?page=123)

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Grue3
Roundabouts are pretty bad for pedestrians. Imagine trying to cross the magic
roundabout on feet from one block to the opposite one. And adding walkways
might be expensive (especially if you want to accomodate wheelchair users).

~~~
roywiggins
You would just cross each street that feeds in/out, right? No cutting across
the islands.

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Normal_gaussian
This is how it works. (British)

~~~
ljf
Yes they often have grass and plants/trees in the middle, which both
discourages people from walking across and stops you seeing ahead when you are
driving, which makes you drive at a more cautious speed.

Or they can be huge and have underpasses like the massive (now demolished)
'hole in the road' in Sheffield, or this beauty in East London (1m25s in)
[https://youtu.be/Smbfm4unjh8](https://youtu.be/Smbfm4unjh8)

~~~
roywiggins
Bristol's bearpit is like that, there are underpasses that take you under the
road and into the "pit" in the middle, so you can cut straight across- much
more convenient and less confusing than attempting to cross the feeder roads.

Bit scary at night, mind.

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kwhitefoot
My home town's claim to fame! Swindon used to be called roundabout city by
some because we have so many.

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KaiserPro
Roundabouts are good in an urban setting. they are a pain in the arse on a
freeway/dual carriage ways.

however, fuck the magic roundabout. Its a hangover from the 60s/70s urban
planning where people decided it'd be great to carve up large amounts of a
town and shit out a huge road in its place. Surrounded by baron lifeless
concrete.

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gkya
Frankly that seems more like a whirlpool.

