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Old April 22nd, 2010, 02:26 AM   #21
Snowguy716
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In Minnesota, the cloverleaf reigns supreme. I don't know if it's because stacks can be dangerous during winter... or they're just cheap... but many of the cloverleafs are much too small for the amount of traffic they handle and so there are always traffic jams around them.

The worst is perhaps the cloverleaf at I-494 and I-35W at the Bloomington/Richfield line.

MNDot has proposed a reconstruction with a "half stack" that would be a hybrid stack/cloverleaf with stack ramps for traffic leaving I-35W and cloverleaf ramps for traffic leaving I-494. While the circles would still slow traffic on 494, it would eliminate the weaving done with circles on both sides with traffic both entering and exiting the freeway over the relatively small bridge.



Courtesy of MNDot
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Old April 22nd, 2010, 02:01 PM   #22
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Why do so few places like the roundabout junctions that are so common here? What are the disadvantages of this type of junction?
I think one major reason is that motorways are tolled in most countries so it makes sense to have trumpet junctions where all traffic is funnelled into one toll station. For motorway to motorway interchanges you should really look beyond roundabouts to stacks or cloverleafs (or its variants) anyway.
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Old April 22nd, 2010, 04:46 PM   #23
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Originally Posted by ChrisZwolle View Post
The British oval roundabout on top of a motorway is generally rare in mainland Europe. As far as I know, we have only two in the Netherlands (Rottepolderplein on A9 and St. Joost on A2)
Interchanges with roundabouts occur in Sweden - especially in urban areas and on the newly constructed roads. Like this, E4 around Uppsala:


Apart from that, there are many different types. The most popular, I think, are diamonds, trumpets and something like that (E4 around Tystberga):


Or a combination of a diamond and that one above (E4 past Hölö):


But that only concerns interchanges with normal roads. Motorway/motorway interchanges... well, there aren't many of those in Sweden. And each of them is unique
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Old April 22nd, 2010, 05:59 PM   #24
Haljackey
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Originally Posted by Snowguy716 View Post
In Minnesota, the cloverleaf reigns supreme. I don't know if it's because stacks can be dangerous during winter... or they're just cheap... but many of the cloverleafs are much too small for the amount of traffic they handle and so there are always traffic jams around them.

The worst is perhaps the cloverleaf at I-494 and I-35W at the Bloomington/Richfield line.

MNDot has proposed a reconstruction with a "half stack" that would be a hybrid stack/cloverleaf with stack ramps for traffic leaving I-35W and cloverleaf ramps for traffic leaving I-494. While the circles would still slow traffic on 494, it would eliminate the weaving done with circles on both sides with traffic both entering and exiting the freeway over the relatively small bridge.

Courtesy of MNDot
Probably because these junctions were constructed a long time ago and have not been upgraded. Cloverleafs are actually much more dangerous than stacks because of the crazy weaving they cause and the chance of rollovers on those tight loop ramps.

By half stack, I assume you mean a cloverstack. Its a good compromise because you get rid of all the weaving and two of the loop ramps (flyovers are much straighter and thus less chance of a rollover).

I don't know if stacks can be dangerous during winter... I could see the flyovers becoming slippery but they are used to a good degree here in Ontario and the rest of Canada. As long as a good de-icing system or whatnot is built into the flyover or gets regular attention deicing trucks, it should be fine.
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Old April 22nd, 2010, 06:05 PM   #25
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I don't know if stacks can be dangerous during winter... I could see the flyovers becoming slippery but they are used to a good degree here in Ontario and the rest of Canada. As long as a good de-icing system or whatnot is built into the flyover or gets regular attention deicing trucks, it should be fine.
The problem in the winter lies in the placement of the snow when the plows go through. The snow usually winds up in the shoulder lanes of the ramp and given the right conditions the snow can harden into ice. Now someone taking the ramp a little too fast can mount the snowbank and become airborne off the ramp or teeter on the guardrail if the snow can't support the full weight of the impacting car. It's happened more than once around Toronto when you get an extended cold snap following a significant snow storm.
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Old April 23rd, 2010, 06:27 PM   #26
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I've heard a different explanation. I've heard that the ground never gets too cold and acts as a big heat sink. Any road that's in the air won't have this benefit and will be more prone to ice. 4 level stack interchanges especially have very long ramps, very high in the air. That said, Detroit has 2-3 four level stack interchanges and Cleveland has 3. Many cities much further to the South including Atlanta, Washington, Philadelphia have less than this.
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Old April 25th, 2010, 05:03 PM   #27
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... though most importantly they give you nice straight sliproads that allow you to accelerate to 70mph as you approach the merge lane
.
Although, because of the shape of those slip-roads, which are mainly unparallel to the carriageway, drivers trying to merge with the traffic very often slowing down instead of fluently speed-up on their end . Reason for that is lack of opportunity to see in car's side mirror a lane they want to merge into, so driver has to turn his head. On junctions with A roads, proper merging lanes almost do not exist.

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The French junctions I find very disorientating, and the slip roads are often very curvy meaning you need to build up speed on the merge lane.
Merging lanes are known, I presume anywhere in the Continental Europe, as this part of road where you are to build your speed efficiently to merge into motorway safely. They are in most cases parallel to motorway, so you can see traffic in your mirrors and have opportunity to jump into first lane in most suitable time not causing others slowing down.

French build roundabout style junctions, as well. However, they are luckily equipped with properly shaped, long merging lanes. The one below from here:

http://maps.google.co.uk/maps?f=q&so...45447&t=k&z=15



And the length of the merging lane.



My favorite junctions? All which let me go through without stopping.

Last edited by piotr71; April 25th, 2010 at 05:56 PM.
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Old April 25th, 2010, 05:47 PM   #28
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Roundabout interchanges still suck though.
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Old April 25th, 2010, 06:44 PM   #29
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Originally Posted by piotr71 View Post
.
My favorite junctions? All which let me go through without stopping.
That should be required for all junctions. No junction should come with traffic lights or stop or yield signs.
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Old April 25th, 2010, 06:47 PM   #30
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Quote:
Originally Posted by piotr71 View Post
.
Although, because of the shape of those slip-roads, which are mainly unparallel to the carriageway, drivers trying to merge with the traffic very often slowing down instead of fluently speed-up on their end . Reason for that is lack of opportunity to see in car's side mirror a lane they want to merge into, so driver has to turn his head. On junctions with A roads, proper merging lanes almost do not exist.
On British motorways most sliproads are dead parallel to the main carriageway, unlike on trumpets where the sliproad is a (sometimes very tight) loop until it becomes the merge lane. It is true however that many merge lanes on A-roads do not have adequate enough merge lanes.

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Merging lanes are known, I presume anywhere in the Continental Europe, as this part of road where you are to build your speed efficiently to merge into motorway safely. They are in most cases parallel to motorway, so you can see traffic in your mirrors and have opportunity to jump into first lane in most suitable time not causing others slowing down.
Most merge lanes are about 200m long. Getting on a motorway from a roundabout junction with nice straight parallel slip roads you are already at 60-70mph so have the whole 200m in which to join the main carriageway. On a trumpet you need to use the first 100-odd metres just to get up to speed, leaving you only with the next 100m in which to join in.
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Old April 25th, 2010, 07:07 PM   #31
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In that context, junctions with the crossing road on top of the motorway are always better. You can use the downhill ramp to pick up speed to merge properly, and use the uphill ramp to slow down to intersect with the crossing road.
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Old April 26th, 2010, 06:06 AM   #32
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Perth uses Diamonds everywhere. They can get very clogged.
While we don't have any freeway to freeway junctions yet, some are in the planning stage, all which seem to be like this-
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Old April 26th, 2010, 01:57 PM   #33
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In that context, junctions with the crossing road on top of the motorway are always better. You can use the downhill ramp to pick up speed to merge properly, and use the uphill ramp to slow down to intersect with the crossing road.
I know of a few junctions where the roundabout of dumbell is placed under the motorway so the slope of the sliproads are the wrong way round. I don't think this really the an issue though since length and shape of the sliproad are much more important IMHO.
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Old April 26th, 2010, 08:00 PM   #34
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Mercifully we don't have a lot of cloverleaf junctions in the UK. As far as I know there are only 2 in Britain: 1 in Livingston, 1 in Redditch and neither on a motorway. The weaving between incoming and outgoing traffic is dangerous, especially at peak periods. There are a few partial ones like the M6/M62 between Liverpool and Manchester, the M25/M40 NW of London or the M4/A329(M) SE of Reading.

There also aren't a lot of motorway-to-motorway trumpet interchanges like you see in continental Europe. The preferred method of motorway termination is the Y-interchange and there are many to chose from. The M1/M18 E of Sheffield, the M5/M6 NW of Birmingham and the M8/M9 W of Edinburgh (to name 3). There are also wierd versions such as the A1(M)/M62 near Pontefract, M3/M27/A33 N of Southampton or the M60/M61/A666 NW of Manchester where extra bits get entangled with the slip-roads.

Then there is the 3-level stacked 'whirl,' a 4-way, free-flow interchange but not as expensive as a 4-level stack. Examples of this include the M3/M25 SW of London, the M11/M25 NE of London and the M60/M62/M602 W of Manchester. There are strange versions of this as well, like the M6/M56/A50 junction between Chester and Manchester.

There are only 3 of the orthodox 4-level stack junctions in Britain (where the slip-roads cross over each other in the middle). The M4/M5 N of Bristol, the M4/M25 W of London and the M23/M25 S of London.

By far the biggest junction in Britain connects the M6/A38(M)/A5127 N of Birmingham. Known as "Spaghetti Junction," it is part 'whirl,' part 'Y,' part stacked roundabout. Amazingly it actually works quite well since the main movement (M6 to A38(M) and vice-versa) has free-flow slip-roads.

By far the worst kind of all-motorway junction, predictably, involves the roundabout. Roundabouts should not be used either as a terminating junction or as a stack in a motorway-to-motorway interchange...but they are, all too frequently. Probably the worst one is the M60/M62/M66 N of Manchester where all the through traffic on the M60 is funnelled onto the roundabout. Other offending stacks include the A1(M)/M18 S of Doncaster, the A1(M)/M25 N of London and the M61/M65 W of Blackburn. Some of the worst ones, like the M1/M62 S of Leeds and the M20/M25 E of London, had partial free-flow roads tunnelled under existing junctions at vast expense. Other offending termination roundabouts include the M4/M32 N of Bristol, the M57/M58/A59/A5036 N of Liverpool (probably the worst) and the M60/M67/A57 E of Manchester. Motorway terminations should use the Y-junction or a simple fork like the M8/M80 in Glasgow.

That pretty much covers the all-motorway interchanges found in Britain. For more information you should check out CBRD or SABRE, both of which are far more comprehensive and knowledgeable than me.

Last edited by jandeczentar; April 26th, 2010 at 09:07 PM.
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Old April 26th, 2010, 08:06 PM   #35
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Originally Posted by jandeczentar View Post
Mercifully we don't have a lot of cloverleaf junctions in the UK. As far as I know there are only 2 in Britain: 1 in Livingston, 1 in Redditch and neither on a motorway. The weaving between incoming and outgoing traffic is dangerous, especially at peak periods.
It helps a lot if there are separate distributor/collector lanes, which should be standard at most high-trafficked cloverleafs in my opinion.

[IMG]http://i41.************/11l08aq.jpg[/IMG]
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Old April 26th, 2010, 09:34 PM   #36
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It helps a lot if there are separate distributor/collector lanes, which should be standard at most high-trafficked cloverleafs in my opinion.
Even with parallel collector/distributor roads the essential problem of the cloverleaf remains. There will still be vehicles trying to move out from the slip road at the same moment as other vehicles are trying to move in onto it, leading to side-on collisions. Also, in the example you gave, the slip roads running parallel to the distributor lanes through the underpass are only about 185m long. That's pretty short, even at relatively low speed. Is that standard or is this an unusually small example?

I know why there are so many (cheapness) but even so, I'm amazed they're so prevalent in Europe given their obvious limitations. I don't know what the accident rate is on junctions like this but I can't imagine they're that safe, especially in heavy traffic and even with the collector/distributor lanes.
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Old April 27th, 2010, 05:26 AM   #37
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Originally Posted by jandeczentar View Post
Even with parallel collector/distributor roads the essential problem of the cloverleaf remains. There will still be vehicles trying to move out from the slip road at the same moment as other vehicles are trying to move in onto it, leading to side-on collisions. Also, in the example you gave, the slip roads running parallel to the distributor lanes through the underpass are only about 185m long. That's pretty short, even at relatively low speed. Is that standard or is this an unusually small example?

I know why there are so many (cheapness) but even so, I'm amazed they're so prevalent in Europe given their obvious limitations. I don't know what the accident rate is on junctions like this but I can't imagine they're that safe, especially in heavy traffic and even with the collector/distributor lanes.
I think that their saving grace is that on a simple cloverleaf with CD's, everybody in the left lane of the CD wants to exit to the right, and everyone entering from the right wants to be on the left, so there's a strong incentive for drivers to cooperate with each other. The CD removes through vehicles from the equation, the drivers of which may be inattentive or indifferent to the needs of merging and exiting drivers. It also gives drivers entering the motorway from the CD a much longer ramp on which to increase their speeds to match those on the motorway before attempting to merge. The same is true in reverse for exiting traffic.
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Old April 27th, 2010, 02:57 PM   #38
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Interchanges with roundabouts occur in Sweden - especially in urban areas and on the newly constructed roads. Like this, E4 around Uppsala:


Apart from that, there are many different types. The most popular, I think, are diamonds, trumpets and something like that (E4 around Tystberga):


Or a combination of a diamond and that one above (E4 past Hölö):


But that only concerns interchanges with normal roads. Motorway/motorway interchanges... well, there aren't many of those in Sweden. And each of them is unique
I don't think we have one standard here in Sweden. They are built in different times and they don't looks like they are so interested how they made one construction in another part of Sweden. They just building one construction which are quite good just for the place its built and looks quite good at the times its built. Sometimes I think they are more interested about constructions from other countries than other parts of Sweden.

So here in Uppsala we have lot of roundabouts but in the rest of Sweden there is not so many of them at the motorways. There is more diamonds and trumpets. There is a few cloverleaf's too. One of them is near the bridge over Öresund.
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Old April 27th, 2010, 03:18 PM   #39
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I like Roundabout Interchanges we have a few in NJ, i also like Trumpets and Parcos.

US 202 @ US 206 / NJ 27


Its controlled by Traffic Lights on the Busy ramps and yields on the none busy ramps. I could not find any other good NJ Roundabout Interchange pictures
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Old April 27th, 2010, 06:44 PM   #40
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I like Roundabout Interchanges we have a few in NJ, i also like Trumpets and Parcos.

US 202 @ US 206 / NJ 27


Its controlled by Traffic Lights on the Busy ramps and yields on the none busy ramps. I could not find any other good NJ Roundabout Interchange pictures
I passed through there just last weekend! I can remember it before that overpass was built.
There must be Google images of circles like Flemington.... (Which is still a "pure" traffic circle with no overpass.)
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