Smallest and largest freeflow interchanges

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ChrisH
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Re: Smallest and largest freeflow interchanges

Post by ChrisH »

Owain wrote: Wed Jul 15, 2020 13:39 This one in Basel seems to squeeze as many movements as possible! The A2/A3 multiplex runs east-west, while the A18 runs through it north-south.


Switz.png
To be honest the whole A2 through Basel feels like one gigantic underground free flow interchange! But that is a particular hotspot as you say.
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Re: Smallest and largest freeflow interchanges

Post by Vierwielen »

Within the UK, the M60/M61/M62 junction has some claim to being a large freeflow incterchange (or is it a series of interchanges?)
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Re: Smallest and largest freeflow interchanges

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The A167(M) exit for the A1058 is freeflow and very compact.
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Re: Smallest and largest freeflow interchanges

Post by danfw194 »

Probably a case of my own perception superseding the actual reality of the size, but the trumpet at J2 A50 always feels nice and big, certainly by UK standards.
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Re: Smallest and largest freeflow interchanges

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ChrisH wrote: Thu Jul 09, 2020 16:01 What are the most compact, or the most sprawling, interchanges you know of?

I'll start off with one contender for each from Qatar:

This one Google Maps OSM link manages free-flow turns and straight-across movements in all directions but has built-up areas right up close to it, and is only about 150m across.

Whereas the new Orbital Highway has some absolutely gargantuan interchanges such as this stack interchange Google Maps OSM link, which is about 600m across at its minimum.
I'm late here, but those are both full stacks, just with a few extra bits and pieces in the first case.

The original four-level interchange in LA is actually not much bigger than the first example. Both at 17 zoom:

https://www.google.co.uk/maps/@25.35206 ... 205056,17z
https://www.google.co.uk/maps/@34.06247 ... 488829,17z

The second example is pretty big for a stack, though still smaller than Colnbrook and Merstham, which are also bigger than most if not all American stacks.

With obvious exceptions like Scotstoun, UK freeflow interchanges are generally on the larger side. I don't recall any four-way interchange bigger than Croft, and I've seen a lot of interchanges [/1000 yard stare]
Last edited by jackal on Sat Sep 19, 2020 21:55, edited 1 time in total.
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Re: Smallest and largest freeflow interchanges

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jackal wrote: Sat Sep 19, 2020 14:01
ChrisH wrote: Thu Jul 09, 2020 16:01 What are the most compact, or the most sprawling, interchanges you know of?

I'll start off with one contender for each from Qatar:

This one Google Maps OSM link manages free-flow turns and straight-across movements in all directions but has built-up areas right up close to it, and is only about 150m across.

Whereas the new Orbital Highway has some absolutely gargantuan interchanges such as this stack interchange Google Maps OSM link, which is about 600m across at its minimum.
I'm late here, but those are both full stacks, just with a few extra bits and pieces in the first case.

The original four-level interchange in LA is actually not much bigger than the first example. Both at 17 zoom:

https://www.google.co.uk/maps/@25.35206 ... 205056,17z
https://www.google.co.uk/maps/@34.06247 ... 488829,17z

The second example is pretty big for a stack, though still smaller than Almondsbury and Merstham, which are also bigger than most if not all American stacks.

With obvious exceptions like Scotstoun, UK freeflow interchanges are generally on the larger side. I don't recall any four-way interchange bigger than Croft, and I've seen a lot of interchanges [/1000 yard stare]
Are you sure? Google maps seem to use different scales for different parts of the world. I measured the second Qatari example as 2.21 km from diverge to merge on the westbound carriageway, while Almondsbury is only 1.15 km on the M4 eastbound. It's a little difficult to decide exactly where to measure from, but the Qatari interchange is about twice the maximum dimension of Almondsbury.

Perhaps a more easily standardisable measurement is the distance between opposite left turn movements (right turn in right hand traffic countries). This probably gives a better idea of the tightness of the turns as merges and diverges are rather variable in how elongated they are. Measuring from (outer) hard shoulder rumble strip to rumble strip the Qatari interchange is 600 m across NE to SW and Almondsbury is 480 m across NW to SE.

Colnebrook is larger than Almondsbury, 590 m NW to SE. Merstham is quite squashed, 685 m NW to SE, but only 415 m NE to SW
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Re: Smallest and largest freeflow interchanges

Post by booshank »

The largest interchange I have personal experience is probably this one in Calgary, Canada. It's about 870 m across between the right turn movements NW to SE.
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Re: Smallest and largest freeflow interchanges

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booshank wrote: Sat Sep 19, 2020 20:13
jackal wrote: Sat Sep 19, 2020 14:01
ChrisH wrote: Thu Jul 09, 2020 16:01 What are the most compact, or the most sprawling, interchanges you know of?

I'll start off with one contender for each from Qatar:

This one Google Maps OSM link manages free-flow turns and straight-across movements in all directions but has built-up areas right up close to it, and is only about 150m across.

Whereas the new Orbital Highway has some absolutely gargantuan interchanges such as this stack interchange Google Maps OSM link, which is about 600m across at its minimum.
I'm late here, but those are both full stacks, just with a few extra bits and pieces in the first case.

The original four-level interchange in LA is actually not much bigger than the first example. Both at 17 zoom:

https://www.google.co.uk/maps/@25.35206 ... 205056,17z
https://www.google.co.uk/maps/@34.06247 ... 488829,17z

The second example is pretty big for a stack, though still smaller than Almondsbury and Merstham, which are also bigger than most if not all American stacks.

With obvious exceptions like Scotstoun, UK freeflow interchanges are generally on the larger side. I don't recall any four-way interchange bigger than Croft, and I've seen a lot of interchanges [/1000 yard stare]
Are you sure? Google maps seem to use different scales for different parts of the world. I measured the second Qatari example as 2.21 km from diverge to merge on the westbound carriageway, while Almondsbury is only 1.15 km on the M4 eastbound. It's a little difficult to decide exactly where to measure from, but the Qatari interchange is about twice the maximum dimension of Almondsbury.

Perhaps a more easily standardisable measurement is the distance between opposite left turn movements (right turn in right hand traffic countries). This probably gives a better idea of the tightness of the turns as merges and diverges are rather variable in how elongated they are. Measuring from (outer) hard shoulder rumble strip to rumble strip the Qatari interchange is 600 m across NE to SW and Almondsbury is 480 m across NW to SE.

Colnebrook is larger than Almondsbury, 590 m NW to SE. Merstham is quite squashed, 685 m NW to SE, but only 415 m NE to SW
Sorry I meant Colnbrook rather than Almondsbury.
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Re: Smallest and largest freeflow interchanges

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booshank wrote: Sat Sep 19, 2020 20:36 The largest interchange I have personal experience is probably this one in Calgary, Canada. It's about 870 m across between the right turn movements NW to SE.
Seems about as big as Croft.

https://www.google.com/maps/@51.1751755 ... 031653,15z
https://www.google.co.uk/maps/@53.42543 ... 576912,15z

So too this outside Edmonton:

https://www.google.co.uk/maps/@53.56644 ... 398541,15z

Really surface area needs to be measured to arbitrate between such cases, though that doesn't help with the issue that in some cases (such as Edmonton) it's unclear where one interchange starts and another ends.
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Re: Smallest and largest freeflow interchanges

Post by booshank »

jackal wrote: Sat Sep 19, 2020 22:02
booshank wrote: Sat Sep 19, 2020 20:36 The largest interchange I have personal experience is probably this one in Calgary, Canada. It's about 870 m across between the right turn movements NW to SE.
Seems about as big as Croft.

https://www.google.com/maps/@51.1751755 ... 031653,15z
https://www.google.co.uk/maps/@53.42543 ... 576912,15z

So too this outside Edmonton:

https://www.google.co.uk/maps/@53.56644 ... 398541,15z

Really surface area needs to be measured to arbitrate between such cases, though that doesn't help with the issue that in some cases (such as Edmonton) it's unclear where one interchange starts and another ends.
Yeah I'm really thinking of 4-way interchanges that are relatively symmetrical in perimeter in both planes, so it works to compare stacks, cloverleaves and hybrids of the two.

This is what I meant by measuring from left turn to left turn (right turn to right turn in RH traffic countries):-

Image

Image
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Re: Smallest and largest freeflow interchanges

Post by booshank »

Abu Dhabi must be in the running for largest trumpet interchange. The loop has a diameter of over 950 m! It's not even clear why it needed to be large as it leads into what looks like a relatively minor road.
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Re: Smallest and largest freeflow interchanges

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booshank wrote: Tue Sep 22, 2020 23:33 Abu Dhabi must be in the running for largest trumpet interchange. The loop has a diameter of over 950 m! It's not even clear why it needed to be large as it leads into what looks like a relatively minor road.
Especially when the left turns at the same junction are so much tighter. Bizarre!
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Re: Smallest and largest freeflow interchanges

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Chris5156 wrote: Wed Sep 23, 2020 10:58
booshank wrote: Tue Sep 22, 2020 23:33 Abu Dhabi must be in the running for largest trumpet interchange. The loop has a diameter of over 950 m! It's not even clear why it needed to be large as it leads into what looks like a relatively minor road.
Especially when the left turns at the same junction are so much tighter. Bizarre!
Such a huge junction is also wasted when one of the roads ploughs into a roundabout.
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Big and complex.
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Re: Smallest and largest freeflow interchanges

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Truvelo wrote: Wed Sep 23, 2020 11:29
Chris5156 wrote: Wed Sep 23, 2020 10:58
booshank wrote: Tue Sep 22, 2020 23:33 Abu Dhabi must be in the running for largest trumpet interchange. The loop has a diameter of over 950 m! It's not even clear why it needed to be large as it leads into what looks like a relatively minor road.
Especially when the left turns at the same junction are so much tighter. Bizarre!
Such a huge junction is also wasted when one of the roads ploughs into a roundabout.
It's in the middle of the desert so land is probably not a concern, and it gives the local supercar owners chance to slow down from 130 to 90...
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Re: Smallest and largest freeflow interchanges

Post by booshank »

Bryn666 wrote: Wed Sep 23, 2020 20:40
Truvelo wrote: Wed Sep 23, 2020 11:29
Chris5156 wrote: Wed Sep 23, 2020 10:58
Especially when the left turns at the same junction are so much tighter. Bizarre!
Such a huge junction is also wasted when one of the roads ploughs into a roundabout.
It's in the middle of the desert so land is probably not a concern, and it gives the local supercar owners chance to slow down from 130 to 90...
It's still a bit weird as it's much larger than any of the motorway-motorway interchanges, which are themselves on the large side but within the bounds of what might be considered "normal" sized. Eg the cloverleaf immediately to the south is bigger than Colnebrook, but could fit inside that loop.
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Re: Smallest and largest freeflow interchanges

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Chris5156 wrote: Wed Sep 23, 2020 10:58
booshank wrote: Tue Sep 22, 2020 23:33 Abu Dhabi must be in the running for largest trumpet interchange. The loop has a diameter of over 950 m! It's not even clear why it needed to be large as it leads into what looks like a relatively minor road.
Especially when the left turns at the same junction are so much tighter. Bizarre!
Actually I think the loop probably matches the design speed on the left turns.

There may also have been some consideration for futureproofing as the minor road leads to a motorway across Yas Island.

That said it is indeed madly oversized.
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Re: Smallest and largest freeflow interchanges

Post by booshank »

The loop is nothing unusual in size, but the left turn and semi-directional right turn movements of the N1 - N4 interchange north of Pretoria are pretty large (2.07 km from diverge to merge northbound). It's interesting how they've used separate bridges for the two right turn movements so that N1 S to N4 gets a much better alignment.

Brasilia has a whole series of tiny cloverleaves. Presumably they were originally intended to be freeflow as it doesn't seem to make much sense to build a cloverleaf with stop signs. Here are a pair next to a normal size cloverleaf.
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Re: Smallest and largest freeflow interchanges

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booshank wrote: Thu Sep 24, 2020 20:16 The loop is nothing unusual in size, but the left turn and semi-directional right turn movements of the N1 - N4 interchange north of Pretoria are pretty large (2.07 km from diverge to merge northbound). It's interesting how they've used separate bridges for the two right turn movements so that N1 S to N4 gets a much better alignment.
That's surely because it's laid out with the intention that it'll eventually be turned into a four-way junction, with N4 continuing east and forming a bypass around north-east Pretoria. The land appears to have already been acquired for the rest of the junction and the property lines are clearly laid out to allow for the left-turns.
Brasilia has a whole series of tiny cloverleaves. Presumably they were originally intended to be freeflow as it doesn't seem to make much sense to build a cloverleaf with stop signs. Here are a pair next to a normal size cloverleaf.
I love these - Brasilia's road network is an absolute triumph of optimism and experimentalism over practicality.
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Re: Smallest and largest freeflow interchanges

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jackal wrote: Thu Sep 24, 2020 16:06 There may also have been some consideration for futureproofing as the minor road leads to a motorway across Yas Island.

That said it is indeed madly oversized.
3 lanes heading northbound out of that junction, merging down to 2 lanes, before gradually merging into the very quiet-looking 4 lane motorway.

I guess the moral of the story is that if you want exceptionally wide, quiet roads with huge junctions, move to an oil-rich desert!
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Re: Smallest and largest freeflow interchanges

Post by Peter Freeman »

It's common for (a) new-build capital cities and (b) cities in oil-rich Modern Arabia, to build transport infrastructure to impress rather than to function cost-effectively. I remember on my first visit to Dubai being driven away from the airport on a D7 bridge over Dubai Creek - with an identical one visible just a kilometre downstream! I was duly impressed. Although I still gaze with wonder at such things whenever I'm there, I see some quite silly road design.

Don't move Owen - you'd be bored stiff after a couple of weeks.
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