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Old September 9th, 2005, 12:44 AM   #21
sargeantcm
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Traffic Circles (or Rotaries) are a totally different breed of intersections than roundabouts. The primary difference is that circles and rotaries are usually designed for speed, and are huge. Modern roundabouts, on the other hand, as designed as a method of "traffic calming", or slowing people down. And they take up just slightly more space than a conventional intersection. They have their downsides too, but that are much safer and efficient IF people know how to drive them. Which in the US is not often.

I know because I've designed a couple of them, they pretty interesting to design, actually.
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Old September 9th, 2005, 08:29 AM   #22
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Quote:
Originally Posted by demanjo
i dont understand the connection?
Well, I'll rephrase: Traffic circles are inefficient, although they can be useful as places to put important landmarks.
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Old September 9th, 2005, 08:56 AM   #23
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Quote:
Originally Posted by firmanhadi
Well, I'll rephrase: Traffic circles are inefficient, although they can be useful as places to put important landmarks.
For example:

Plaza Cibeles in Madrid:



Place de Charles de Gaulle, Paris

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Old September 9th, 2005, 10:06 AM   #24
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Quote:
Originally Posted by sargeantcm
Traffic Circles (or Rotaries) are a totally different breed of intersections than roundabouts. The primary difference is that circles and rotaries are usually designed for speed, and are huge. Modern roundabouts, on the other hand, as designed as a method of "traffic calming", or slowing people down. And they take up just slightly more space than a conventional intersection. They have their downsides too, but that are much safer and efficient IF people know how to drive them. Which in the US is not often.

I know because I've designed a couple of them, they pretty interesting to design, actually.
Exactly. If you do a little bit of legwork in the research you'll find that they're fundamentally different. The biggest different in my opinion is not size - There's plenty of roundabouts that serve as one giant freeway interchange:

and there's numerous roundabouts about 7 feet (2 metres) in diameter - there's two, a very short drive from me.


The real difference lies in the way they're used. Rotaries or traffic circles don't exist in Australia - well that I know of anyway. But rotaries work on the basis that any traffic entering into the rotary have right-of-way, so any traffic already in the circle has to give way/yield to entering traffic. Rotaries are also chaotic because there are no lanes for people to stick to leading to accidents. Also drivers are unwilling to yield when they believe (rightly or wrongly) that the traffic entering won't cross their path. Also in a rotary you tend to weave a bit to get to your exit.

When approaching a roundabout, you must give way to any traffic already in the roundabout. You can tell which way they're going by looking at their indicator. This allow queues to be on the approach rather than in the circle itself - which could cause the traffic circle to have severe blockages because there's too much traffic in the circle and no-one in the circle can get out.

That animation is not really correct, because the lanes within the roundabout aren't shown. moist roundabouts are single-lane so you don't traffic within the roundabout crossing paths. But how double-laned roundabouts work perfectly confounds me. But what you do is when approaching and entering the round about from say the left lane, you stay in the left lane when moving around the roundabout. Generally, the left lane is for traffic going straight or turning left, and the right lane is for going straight or turning right. And you don't get too much weaving because all aproaches must giveway/yield to existing traffic anyway so you don't get that mess you see in rotaries.

See the road rule's for New South Wales Roads and Traffic Authority for a guide on how to use a roundabout. There's some neat diagrams for you to follow too. http://www.rta.nsw.gov.au/rulesregul...undabouts.html
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Old September 9th, 2005, 10:48 AM   #25
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There are plenty of roundabouts on both arterial and local roads where I live.

They work reasonably well for cars but there is still a hangover from an old "Give way to the right" intersection management that applied here until the 1970s. Many drivers approach the roundabouts at 40 or 50kph and expect everyone ahead of them (including those already at the intersection) to give way.

The biggest losers with local roundabouts are pedestrians; where they used to have right of way on the priority road at an intersection, it has been taken away and they must give way to all traffic. In addition, the creation of large traffic islands has eaten into footpath space and forced pedestrians around a longer crossing route, sometimes with reduced visibility of approaching traffic.

I wonder why it is necessary to install an island to create a roundabout? - The roundabout traffic movement principles would still apply if there were a only a pole and /or a small island in the middle of the intersection and strict approach speed limits applied.
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Old September 10th, 2005, 07:39 AM   #26
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Round abouts are great for small suburban roads that handle moderate traffic but when they use them for big roads that handle heave traffic they are less then desirable. They are most definately better then traffic lights though especially in the suburban areas.
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Old September 10th, 2005, 12:47 PM   #27
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Quote:
Originally Posted by sargeantcm
They have their downsides too, but that are much safer and efficient IF people know how to drive them. Which in the US is not often.
Lots of people are saying that drivers in the US don't know how to use them, don't you learn that in your driving test?

Quote:
Originally Posted by Daffy
I wonder why it is necessary to install an island to create a roundabout? - The roundabout traffic movement principles would still apply if there were a only a pole and /or a small island in the middle of the intersection and strict approach speed limits applied.
There are many "mini-roundabouts in the UK, often just a painted circle in the middle of the intersection, normal roundabout rules apply



This is the "King of Roundabouts" the Magic Roundabout in Swindon, UK. Five mini-roundabouts surronding a larger hub roundabout!!



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Old September 10th, 2005, 06:08 PM   #28
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How do you think about this roundabout? Unfortunately I do not know, where it is! ( http://www.brueckenweb.de/Datenbank/...usgabe_lex.php )

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Old September 10th, 2005, 06:40 PM   #29
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damm that thing in Swindon looks confusing but i would disagree its the king of roundabouts, that one has to go to the Arc de triomph in Paris, it's also gotta be the most dangerous, people drive at it and dn't even hit the brake they just drive into a six lane roundabout with thier hand constantly on the horn.
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Old September 11th, 2005, 08:11 AM   #30
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Quote:
Originally Posted by Jonesy55
Lots of people are saying that drivers in the US don't know how to use them, don't you learn that in your driving test?
Not in Illinois and New York.
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Old September 11th, 2005, 08:16 AM   #31
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I feel they are outdated and cause accidents.

Suburban streets that don't have the numbers to support traffic lights, thats fine but major roads really shouldn't have roundabouts.
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Old September 14th, 2005, 12:41 AM   #32
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In the UK we pretty much have to have them because we have lots of roads crossing all at weird angles and stuff. Obviously you have to learn them for your driving test so the generally work out more effiecient than traffic lights because you only have to stop sometimes and if you do stop its generally only for a few seconds. As has been said on roundabouts where many people take the same exit you often get traffic lights or temporary traffic lights that operate during rush hour.

They are particulaly fun to go round sideways at 4 am
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Old September 14th, 2005, 12:45 AM   #33
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Quote:
Originally Posted by JDRS
If people know what they're doing they are a good idea. As aatbloke says traffic lights can be put on roundabouts if it becomes too busy at certain periods. They're used alot here, and Milton Keynes is renowned for the number of roundabouts they have. I have a roundabout near me nicknamed the "magic roundabout" that goes in two directions. Confuses many people.
I live near Milton Keynes, too many roundabouts!!!!!! Everywere looks the same, so easy to get lost, overall a characterless dump
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Old September 14th, 2005, 04:58 AM   #34
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Roundabouts were great for big cities back when people still rode horses, because horses were smart enough not to walk into into one another. For cars... well... the paradigm just doesn't quite work as well. The only new ones that seem to get built in the US are in residential neighborhoods that put them there PRECISELY because they screw up the traffic flow and scare drivers away.

There are a few wacky 5 and 6-way intersections in the Miami area that apparently used to be roundabouts when they were built back in the 1920s and 1930s... but now they have traffic lights that are almost as dysfunctional. There's just no good way to handle a busy 5-way intersection, period, and the idiot who put it there it in the first placee (apparently, because the developer thought they looked pretty on the map and marketing brochures) hopefully had an extra-toasty spot in hell reserved for him

Last edited by miamicanes; September 14th, 2005 at 05:05 AM.
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Old September 14th, 2005, 08:54 PM   #35
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I like roundabouts, only in residential areas and suburbs, but not in heavily urban/inner city centers.
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Old September 15th, 2005, 02:01 AM   #36
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Quote:
Originally Posted by Jonesy55

This is the "King of Roundabouts" the Magic Roundabout in Swindon, UK. Five mini-roundabouts surronding a larger hub roundabout!!



Just looking at these circles makes me wanna barf, makes me sick.
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Old September 15th, 2005, 03:37 PM   #37
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Where I live, in the Netherlands, there are roundabouts everywhere! I really like them. Last year I was in Caīro and this is a very busy roundabout there.



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Old September 17th, 2005, 02:17 AM   #38
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here is a "bog standard" roundabout you will come across on pretty much any journey you make in the UK outside of the town centres. They are nice and simple I think.
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Old September 18th, 2005, 03:45 PM   #39
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Roundabout in Melbourne with Tram tracks going through the middle:
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Old September 26th, 2005, 02:26 PM   #40
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Quote:
Originally Posted by NerveAgent
here is a "bog standard" roundabout you will come across on pretty much any journey you make in the UK outside of the town centres. They are nice and simple I think.
These are everywhere in Australia too - it's a lot safer than a plain intersection where you're giving way to high speed traffic, and they generally get replaced with traffic lights when there is enough traffic. And like in the photo above, they're good at intersections that have several roads forking out in different directions, where traffic lights would be very confusing.

Roundabouts are fine if people know how to use them properly (and use their indicators too). It's a different story for pedestrians and cyclists, but a few have pedestrian crossings on all approaches.
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