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Old April 20th, 2010, 01:33 AM   #1
NCT
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Which type of junctions are common in your country, and which is your preferred type?

I haven't found another thread on this topic but if there is feel free to lock or merge this thread.

I recently went on a road trip through France to Spain and I noticed how motorway junctions are distinctly different in France, Spain and in the UK.

In France and Spain where motorways are tolled the trumpet type is the most cost-effective and indeed most common.



Usually a motorway-to-road interchange consists of a link road connecting the two, with a trumpet interchange at the motorway end and a flat junction at the ordinary-road end. An example of such an interchange is this:

http://maps.google.co.uk/?ie=UTF8&ll...13711&t=k&z=16

Even motorway to motorway interchanges seem to consist of two trumpets connected by a link road:

http://maps.google.co.uk/?ie=UTF8&ll...,0.027423&z=15


In the UK by far the most common is the roundabout, and dumbell and three-level roundabout junctions easy to find too. A few really busy junctions are of the more free-flowing whirlpool or 4-level stack types.

Roundabout:



Dumbell:



Three-level roundabout:



Whirlpool:



Four-level stack:



In China most motorway to road interchanges seem to be of the trumpet type due to toll-booth considerations. Motorway to motorway junctions are mostly 4-level stack, whirlpool or (partial-)cloverleaves.

Parcial cloverleaves:



Which type of junctions are prevelent in your country and which ones are your favourite?
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Old April 20th, 2010, 09:16 AM   #2
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France doesn't have many 4-way interchanges, most are 3-ways. Therefore, there are almost no cloverleafs in France, or stacks for that matter. Germany has more like a grid system, and cloverleafs are far more common. Cloverleafs are also common in the Netherlands.

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)
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Old April 20th, 2010, 05:16 PM   #3
Bartolo
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In Ontario, every interchange is a Parclo and all 4 way interchanges between freeways are cloverstacks expect the 400 and 407 is a stack
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Old April 20th, 2010, 05:37 PM   #4
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*Parclo = Partial Cloverleaf
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Old April 20th, 2010, 07:53 PM   #5
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In the United States there is a little bit of everything and they vary not only state by state but county by county. Budgets are a very big consideration in the design.

Where I live, in South Florida, we had cloverleaves and partial cloverleaves when expressways began to be built between the 1950's to the 1970's.

As the population grew and more expressways were built or widened, the interchange designs became more ad hoc according to the location and the availability of land. Some of the ramps in recently-built interchanges end in intersections with traffic lights, which slows down the traffic that, in the past, effortlessly merged down the cloverleaf ramps.

At the Golden Glades interchange, where Interstate 95, State Road 826 (Palmetto Expresway), State Road 7, US 441, State Road 9 and the Florida Turnpike join, the design is like strands of spaghetti or silly string thrown together over four decades in a poorly thought out ad hoc design:


There is also an interchange in far western Broward County where Interstates 75 joins Interstate 595, State Road 869 (Sawgrass Expressway) and State Road 84 which is a mix between whirlpool and multilevel stack designs:


In both of those interchanges, at least three limited-access highways (expressways) join with each other and with regular open access roads.
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Old April 20th, 2010, 07:57 PM   #6
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Spain has a shitload of incomplete interchanges. Almost every village along an Autovía has at least two partial interchanges where you can only go on two directions on both sides of town.
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Old April 20th, 2010, 09:12 PM   #7
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I prefer the full cloverleaf design because it doesn't interfere with the free flow of traffic (provided that it has adequate merging zones at the tangential points of the circular ramps).

Here is an example of a perfectly good full cloverleaf interchange that was converted into a partial cloverleaf (with traffic lights that hinder traffic) when the expressway was widened and the ramps redone. It's in Miami, Florida, USA at the intersection of State Road 826 (also know as the Palmetto Expressway) and State Road 90 (also known as US 41, Tamiami Trail, SW 8 Street, and Calle Ocho).

Before the remodeling of the interchange, you could connect from any direction in one road to any direction in the other road. See the area in 2002:


Now, with the elimination of two ramps, you have to wait at traffic lights to go from northbound SR 826 to westbound SR 90 and from westbound SR 90 to southbound SR 826. In addition, you can no longer make U-turns using the ramps. See the interchange in 2010:
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Old April 20th, 2010, 10:23 PM   #8
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I like to call stacks and stuff like this "concrete knots"
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Old April 20th, 2010, 10:39 PM   #9
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Just about everything here is a parclo:


But I prefer stack... but its kinda expensive and excessive to build one at every single interchange.
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Old April 20th, 2010, 10:53 PM   #10
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Stacks are not necessarily larger in area than a cloverleaf with a collector/distributor setup. Only if you are gonna include more than 4 levels, it becomes larger because you need longer ramps with a wider curvature.
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Old April 20th, 2010, 11:15 PM   #11
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Quote:
Originally Posted by Haljackey View Post
Just about everything here is a parclo:
...

But I prefer stack... but its kinda expensive and excessive to build one at every single interchange.
Heh stacks aren't really built between a regular road and a freeway (like in your picture). Parclos are a great compromise IMO. All entrances to the freeway are free-flowing, but the exits have traffic lights.

Of course, between freeways stacks have the most capacity, but as you said, they are very expensive to build.
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Old April 20th, 2010, 11:25 PM   #12
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UK Motorway junctions are almost overwhelmingly Roundabout type (roundabout above or below the motorway. We just seem to have an obsession with roundabouts, probably because they work so well! (So long as they aren't signal controlled).

We have very few diamond junctions like those seen in the USA.



The few situations where two motorways intersect in a 4-way junction in the UK are covered by 4-level stacks or turbines.
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Old April 21st, 2010, 06:54 AM   #13
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In western Canada, Diamond type interchanges predominate. Exit the motorway at the slip road and travel to the junction with the cross road. Major ones for the most part, have traffic lights. The advantage to these types, aside from their simplicity, are, that if required, traffic can be diverted down the slip road, and up the entrance ramp on the far side.
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Old April 21st, 2010, 06:58 AM   #14
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We've had lots of threads on this. In america, the most common expressway - road interchanges, especially in the suburban areas, are diamonds. Sometimes a "trumpet" is used instead. Common expressway interchanges include the cloverleaf and various types of partial or full stack interchanges.
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Old April 21st, 2010, 07:22 AM   #15
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Quote:
Originally Posted by Haljackey View Post
But I prefer stack... but its kinda expensive and excessive to build one at every single interchange.
Quote:
Originally Posted by ChrisZwolle View Post
Stacks are not necessarily larger in area than a cloverleaf with a collector/distributor setup. Only if you are gonna include more than 4 levels, it becomes larger because you need longer ramps with a wider curvature.
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Heh stacks aren't really built between a regular road and a freeway (like in your picture). Parclos are a great compromise IMO. All entrances to the freeway are free-flowing, but the exits have traffic lights.

Of course, between freeways stacks have the most capacity, but as you said, they are very expensive to build.
The thread asked me which my preferred type is. My answer is stack, even if it is with a minor road . No stop lights, weaving or loop ramps. Realistically that makes absolutely 0 sense because they are only needed with major junctions with another highway if the conditions are right.
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Old April 21st, 2010, 03:07 PM   #16
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Stacks are no doubt one of the best for very busy junctions. IMO roundabouts are probably the best for other junctions - very simple to navigate and no flat junctions (in the traditional sense), though most importantly they give you nice straight sliproads that allow you to accelerate to 70mph as you approach the merge lane. 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.
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Old April 21st, 2010, 06:57 PM   #17
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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?
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Old April 21st, 2010, 07:21 PM   #18
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You need to construct two bridges over the motorway, which - in general - is more expensive than an interchange with one bridge. You also see a lot of interchanges with two roundabouts at either side and one bridge in between across the motorway.
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Old April 21st, 2010, 07:32 PM   #19
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Those are 'dumbell' junctions aren't they?

I'm guessing a 'roundabout on top' is still much cheaper than a stack or turbine though and uses less land than any cloverleaf variant.
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Old April 21st, 2010, 07:42 PM   #20
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In Ohio, they're replacing a number of cloverleaf interchanges with these:

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