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Old September 3rd, 2015, 09:22 PM   #941
MattiG
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Quote:
Originally Posted by Kanadzie View Post
I'm not sure an interchange would work well for these "magic roundabouts". There seems to be like five or seven different roads coming into the area, with no clear through-route. Typical interchange would only be four roads with at least one clear through route. To handle seven roads you'd have maybe interchange and extra roundabouts
It is not an mission impossible to create a 5-way interchange, if we can drop the constraint of having a clear through-route. Many 3-way interchanges are triangle-shaped, free of such a constraint.

The more roads there meet, the less importance is the through-road principle. In this symmetric 5-way scheme, each incoming road is divided into two with only a 36-degree turn:



In the real world, the 5-way interchanges are typically spaghetti-like unstructured ones, or divided into two interchanges.
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Old September 3rd, 2015, 11:39 PM   #942
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Some of the roundabout interchanges in Sweden are badly designed. A few weeks ago, I drove on the exit 111 on E4 (Linköping West) from the west and turned to the north, and felt somewhat uncomfortable.



The area of the interchange is huge, about 60 hectares. It is more than six times more than the area of the newest dogbone interchanges of the new E18 section in Finland. Still, the curvature of the ring may lead to surprises.

The radius of the exit ramp from the west is about 250 meters. No problem with that. But the ramp joins a very short weaving area: The exit ramp leads out of the ring, and those ones turning to the north must suddenly change two lanes to the left within 100 meters only.



However, that is not the last surprise. The left curve is far too tight, its radius is 60 meters only. After surviving that, you are on the lane leading back to the E4. In order to exit the ring to 34 Motala, another lane change is needed, this time to the right.
Technically it's not a roundabout interchange, but a traffic circle. Traffic already in the circle doesn't have priority, but rather those changing lanes have to yield. It's one of, if not THE worst interchange on the E4 or even in Sweden as a whole.

This image illustrates the problem with that interchange:
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Old September 4th, 2015, 12:47 AM   #943
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Does it exist somewhere?
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Old September 4th, 2015, 01:00 AM   #944
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OMG the weaving
It's so pretty though
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Old September 4th, 2015, 11:59 AM   #945
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Does it exist somewhere?
Never seen. It would combine the drawbacks of a cloverleaf and a stack: tight loop ramps, needs much space, challenging weaving, and high cost caused by several bridges. But beautiful it would be!
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Old September 4th, 2015, 12:40 PM   #946
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Technically it's not a roundabout interchange, but a traffic circle. Traffic already in the circle doesn't have priority, but rather those changing lanes have to yield. It's one of, if not THE worst interchange on the E4 or even in Sweden as a whole.

Well don't forget it's made like that cause 80% of traffic who enter is North - South bound, thus it give priority to this traffic over E4.

Now, could it be improved, hell yeah, but it's not as bad as ppl make it out to be, trust me I used to be a resident of Cloetta Town.
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Old September 4th, 2015, 03:08 PM   #947
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Technically it's not a roundabout interchange, but a traffic circle. Traffic already in the circle doesn't have priority, but rather those changing lanes have to yield.
Well... In the US Federal standards, there is a distinction between the terms "traffic circle" and "modern roundabout". Outside US, this naming thing is more or less of academic semantics. In many dictionaries, "a traffic circle" and "a roundabout" are synonyms. In this discussion thread about interchange structures, the question about who has to yield is more or less irrelevant.

In this structure, the incoming vehicle does not need to yield. However, this is a partial truth only: All incoming lanes lead out of the structure at the next exit. Those ones to continue driving in the circle, are needed to change the lane, thus yield. Therefore, there are good reasons to call the structure a roundabout even within the context of the US Federal terminology. Or a roundabout equipped with four non-separated fast paths. :-)

BTW, when was that roundabout built? Was it originally a level crossing and later converted to an interchange?
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Old September 4th, 2015, 04:53 PM   #948
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It is kind of weird since we hear a lot of that pushing of that point on e.g. roadgeek forums

But is there any "traffic circle" operating in the whole USA?
There are some with YIELD signs on the approach roads that are roundabout.
The ones that are larger, older, almost always have traffic lights, so really they are neither but just a road that happens to be round.

I am not sure if any American or Canadian would even understand the "priorité à droite" you'd need to use a "traffic circle" without crashing immediately now that the situation is so extremely rare (every intersection has lights or signs assigning priorities) Essentially all roads are considered priority roads.
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Old September 4th, 2015, 06:25 PM   #949
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BTW, when was that roundabout built? Was it originally a level crossing and later converted to an interchange?
It was never a level crossing but built from scratch from what I know. I'm guessing it was completed in 1979 when the Vikingstad-Linköping stretch was built. Not sure what it looked like (or if it existed) from 1975 to 1979, which is when the Linköping bypass was completed afaik. Sources and/or pictures to confirm or deny this are very welcome.
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Old September 5th, 2015, 01:19 AM   #950
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It is good to recognize that the UK is the largest outdoor museum in the Europe, and populated by zillions on nimbys. It is hard to reach a consensus to build anything involving a bridge, especially in built-up areas. Therefore, the roundabout is the basic element outside the motorways. If the capacity of a traditional roundabout is exhausted, more creative ideas are welcome.

The basic idea of those magic roundabouts is simple: the inner ring provides with a fast access to the exits at the right-hand size without driving the whole roundabout, thus improving the throughput. However, there is some gap between the theory and the real word: Quite many people say the structure is terrifying. There are not many such roundabouts built.

I travel to work in this city - Milton Keynes every work day, and it is one of the only cities in the UK where most of the grid roads have posted national speed limit - that is 60mph on single carriageway (non-divided) or 70 mph on dual carriageway sections (divided). The roads on the grid are also numbered by as either V or H roads.

The roundabouts are very frequent, usually every 1km or so or 0.5 km as the main grid roads pass the city centre. With all those roundabouts, it's a roumour that people that regularly drive in Milton Keynes experience uneven tyre wear because of the roundabouts, with the outer shoulder of the left side tyres becoming worn quickly.

The road network was designed as a "distorted grid" to distribute traffic and minimise congestion. This works to a degree except where these routes converge towards the M1. So it's not unusual to be queueing to get onto the M1 about a mile from the junction.
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Old September 5th, 2015, 01:55 AM   #951
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Strange place Milton Keynes, for being in Europe. This urban structure is typically North-American.
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In real life, electronic toll collection was first introduced in Bergen, Norway in 1986, and well into the 21th century many countries still struggle to implement it.
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Old September 5th, 2015, 04:56 AM   #952
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Not really... sort of... but way too many roundabouts and the major roads are all wonky, and those horrid English rowhouses / terraces everywhere
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Old September 5th, 2015, 10:17 AM   #953
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Originally Posted by Kanadzie View Post

It is kind of weird since we hear a lot of that pushing of that point on e.g. roadgeek forums

But is there any "traffic circle" operating in the whole USA?
There are some with YIELD signs on the approach roads that are roundabout.
The ones that are larger, older, almost always have traffic lights, so really they are neither but just a road that happens to be round.

I am not sure if any American or Canadian would even understand the "priorité à droite" you'd need to use a "traffic circle" without crashing immediately now that the situation is so extremely rare (every intersection has lights or signs assigning priorities) Essentially all roads are considered priority roads.
Also here in Italy traffic circles are almost never used anymore, we use roundabouts instead. They were more common in the past (as the first roundabouts were introduced in Italy only in 1989).
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“The transponder’s personalised signal would be picked up when the car passed through an intersection, and then relayed to a central computer which would calculate the charge according to the intersection and the time of day and add it to the car’s bill” - Nobel Economics Prize winner William Vickrey, proposing a system of electronic tolling for the Washington metropolitan area, 1959
In real life, electronic toll collection was first introduced in Bergen, Norway in 1986, and well into the 21th century many countries still struggle to implement it.
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Old September 6th, 2015, 10:20 PM   #954
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Quote:
Originally Posted by Kanadzie View Post

It is kind of weird since we hear a lot of that pushing of that point on e.g. roadgeek forums

But is there any "traffic circle" operating in the whole USA?
There are some with YIELD signs on the approach roads that are roundabout.
The ones that are larger, older, almost always have traffic lights, so really they are neither but just a road that happens to be round.

I am not sure if any American or Canadian would even understand the "priorité à droite" you'd need to use a "traffic circle" without crashing immediately now that the situation is so extremely rare (every intersection has lights or signs assigning priorities) Essentially all roads are considered priority roads.
I know that there is an open dispute about the terminology.

Anyway, the word "roundabout" is much older than a specification of a "modern roundabout" (yield-at-entry, etc). The word "roundabout" dates back to early 20th century when the first such junctions were built in the UK. However, the yield-at-entry rule was declared in the UK no earlier than in 1966. Therefore, I would use the "roundabout" as a generic term, and follow the US Federal terminology "modern roundabout" when the yield-at-entry rule is a relevant within the context of the discussion.

(BTW, the yield-at-entry is not the only qualifying factor in the US. There are certain rules related to geometry, too.)

It is good to understand that the US Federal term is "modern roundabout" to distinguish it from the generic term. There are various interpretations of the terminology around the World, and even across the US states. For instance, there is no such term as "traffic circle" in the official language of the UK Department of Transport.

That is why I tend to avoid treating the US federal terminology as the truth, the whole truth, and nothing but the truth.
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Old September 14th, 2015, 10:07 AM   #955
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Strange roundabout with the cycle lane in the middle of the roadway in Lelystad, NL.

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Old September 14th, 2015, 10:55 AM   #956
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Strange roundabout with the cycle lane in the middle of the roadway in Lelystad, NL.

WTF? Why?
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Old September 14th, 2015, 11:15 AM   #957
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Strange roundabout with the cycle lane in the middle of the roadway in Lelystad, NL.

[]http://i.imgur.com/Al3wcRW.jpg[/img]
Not even drunk i will use a bike there O_O
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Old September 14th, 2015, 11:26 AM   #958
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Not even drunk i will use a bike there O_O
It's actually a great way to tell cyclists they should use a middle of the lane instead of keeping to the right. It's much safer and a proper way to clear a roundabout. I always assume "car position" (middle of the lane) when entering and going through roundabouts.

Look here for more info: https://ec.europa.eu/energy/intellig...ections_en.pdf
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Old September 14th, 2015, 11:59 AM   #959
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There are loads of roundabouts in The Netherlands with the cyclepaths on the roundabout but to the side, they're not more accident-prone at all so this is a solution for nothing and basically a way to annoy car drivers. There's no way I'd be driving in the middle of the roundabout there on my bike.
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Old September 14th, 2015, 12:02 PM   #960
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There are loads of roundabouts in The Netherlands with the cyclepaths on the roundabout but to the side, they're not more accident-prone at all so this is a solution for nothing and basically a way to annoy car drivers. There's no way I'd be driving in the middle of the roundabout there on my bike.
How can allowing cars to pass you (and potentially hit you when they try to exit and you don't) be more safe than this?

Drivers are notorious at not checking blind corners when exiting roundabouts. Driving in the middle of the lane on small roundabouts is much safer. It's not like cyclists are much slower than cars on roundabouts, so I don't see how would it annoy drivers...
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