Diverging Diamonds

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Peter Freeman
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Re: Diverging Diamonds

Post by Peter Freeman »

Construction of Australia's first DDI is well underway. Here's a fly-through video simulation.

https://www.youtube.com/watch?v=X0MZAPc ... e=youtu.be
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Bryn666
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Re: Diverging Diamonds

Post by Bryn666 »

Peter Freeman wrote: Sat Mar 23, 2019 13:14 Construction of Australia's first DDI is well underway. Here's a fly-through video simulation.

https://www.youtube.com/watch?v=X0MZAPc ... e=youtu.be
Tidy signs, markings, none of that stupid three hundred acres of hatching at tiger-tails...

Sigh, we are being left behind in the UK.
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Truvelo
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Re: Diverging Diamonds

Post by Truvelo »

Bryn666 wrote: Sat Mar 23, 2019 13:24 Sigh, we are being left behind in the UK.
Not only in the real world but the virtual world too. Those graphics are getting close to being realistic and I even see pedestrians moving on the sidewalks.
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Peter Freeman
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Re: Diverging Diamonds

Post by Peter Freeman »

AU's first DDI opens 2020. The second has just been announced. It will be in Bald Hills, a northern suburb of Brisbane, QLD. It will be a modification of an existing signalised close diamond.
(edit 2020: now under construction)
(edit 2022: now complete)
Last edited by Peter Freeman on Fri Apr 08, 2022 16:00, edited 2 times in total.
tom1977
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Re: Diverging Diamonds

Post by tom1977 »

Truvelo wrote: Sat Mar 23, 2019 19:04
Bryn666 wrote: Sat Mar 23, 2019 13:24 Sigh, we are being left behind in the UK.
Not only in the real world but the virtual world too. Those graphics are getting close to being realistic and I even see pedestrians moving on the sidewalks.
I believe this is an Arup design and visualisation.
Peter Freeman
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Re: Diverging Diamonds

Post by Peter Freeman »

Apparently there are now over 150 DDIs open or under-construction worldwide. Several commissioned each year recently in the USA, with an increasing proportion of new builds.
Last edited by Peter Freeman on Mon May 04, 2020 08:39, edited 1 time in total.
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Bryn666
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Re: Diverging Diamonds

Post by Bryn666 »

And here we are in the UK ignoring such advances in favour of giant signal controlled roundabouts.

Innovation terrifies the UK doesn't it?
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MotorwayPlannerM21
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Re: Diverging Diamonds

Post by MotorwayPlannerM21 »

Bryn666 wrote: Wed Oct 16, 2019 13:56 And here we are in the UK ignoring such advances in favour of giant signal controlled roundabouts.

Innovation terrifies the UK doesn't it?
Of course the question is how many locations in the UK are actually suitable for DDIs?
"All roads lead to Rome"
What about the M25?

The A205 - The road to... oh wait I should've turned right back there!
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ScottB5411
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Re: Diverging Diamonds

Post by ScottB5411 »

One issue I can see with DDI's in the UK would be the inability for traffic to make the left and right turns off the motorway on red, I don't believe flashing amber arrows are allowed in the UK are they, like they are in Ireland, say. This would hinder traffic leaving a motorway and decrease the throughput that other countries achieve.
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Re: Diverging Diamonds

Post by Bryn666 »

ScottB5411 wrote: Wed Oct 16, 2019 14:17 One issue I can see with DDI's in the UK would be the inability for traffic to make the left and right turns off the motorway on red, I don't believe flashing amber arrows are allowed in the UK are they, like they are in Ireland, say. This would hinder traffic leaving a motorway and decrease the throughput that other countries achieve.
Quite easily achieved with simple give way lines and pedestrian demand stages on signals...

M60 J7 is a screamingly obvious candidate for a DDI.
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Stevie D
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Re: Diverging Diamonds

Post by Stevie D »

ScottB5411 wrote: Wed Oct 16, 2019 14:17 One issue I can see with DDI's in the UK would be the inability for traffic to make the left and right turns off the motorway on red, I don't believe flashing amber arrows are allowed in the UK are they, like they are in Ireland, say. This would hinder traffic leaving a motorway and decrease the throughput that other countries achieve.
I don't see that being a problem. A lot of exit slip roads are now signal controlled, and that generally results in shorter queues on the slip roads (ie more throughput) than where traffic had to give way at a roundabout or priority junction. The advantage about DDI is that it reduces the number of conflict points, so that all signal controlled flows get ≈50% green time (minus intergreen periods), whereas in other layouts they might get significantly less if there are more than two flows to be accommodated.

And depending on the layout, some or all of them could be give ways rather than signal control, allowing exactly the same "go" time as if they were signal controlled plus any gaps that drivers find in what would have been the "red" time.
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Re: Diverging Diamonds

Post by ScottB5411 »

I'm well aware of the advantages of DDI's, the St Louis area has several of them and they have all but eliminated traffic issues at the junctions they have been installed. The ability for traffic to turn on a red light further eliminates queues back onto then interstate and therefore increases throughput of traffic, that is from personal observation whilst driving my car through DDI intersections.
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Re: Diverging Diamonds

Post by Glen »

There's no need to turn on red, we have junctions with priority left turns where other flows are signalled, it just needs an island to separate the lane with give way lines from the signalled lane.
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Re: Diverging Diamonds

Post by Peter Freeman »

ScottB5411 wrote: Wed Oct 16, 2019 14:17 One issue I can see with DDI's in the UK would be the inability for traffic to make the left and right turns off the motorway on red, I don't believe flashing amber arrows are allowed in the UK are they, like they are in Ireland, say. This would hinder traffic leaving a motorway and decrease the throughput that other countries achieve.
Scott, in the USA, including in your state MO and in the KC area, there is great variety in whether the off-ramps are signalised or not. And where they are not signalised, there is variety in how the merges/diverges are marked (yield, lane add/drop, acceleration/deceleration lanes, etc). Virtually all implementations have on-demand signalisation of generous pedestrian crossings.

This issue is not a problem. The same concern could be expressed about any signalised diamond, or indeed any signalised roundabout.
Peter Freeman
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Re: Diverging Diamonds

Post by Peter Freeman »

Construction of Australia's third DDI should commence late this year. It will be at Exit 87 of the Pacific Motorway, near to the Gold Coast in SE Queensland. It will replace a 2-bridge roundabout that is congested and that can cause mainline queuing on this busy freeway.
Video simulation -
https://www.youtube.com/watch?v=enk5HbC ... e=emb_logo

The first DDI will complete this year, and the second is in planning. Both in or near Brisbane.

(edit 2021: QLD's first is operational, the 2nd and 3rd are both under construction)

A fourth has been revealed in the EIS for Sydney's proposed Western Harbour Tunnel. It will be at Falcon Street, which overpasses the Warringah Freeway just north of the harbour bridge. The freeway here peaks at over 250,000 vehicles per day.
Video simulation (select "Falcon Street Interchange") -
https://v2.communityanalytics.com.au/rms/wht/gallery
Last edited by Peter Freeman on Sat Dec 04, 2021 21:28, edited 2 times in total.
Peter Freeman
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Re: Diverging Diamonds

Post by Peter Freeman »

Most USA DDI's have been conversions from standard signalised diamonds, but I've just seen (what I think is) the first cloverleaf converted to a DDI. It is on the I70 in Pennsylvania. This is interesting because -

(a) it's changed from fully-free-flow on both crossing roads to non-free-flow on one of them, but has been deemed to work better anyway;

(b) cloverleaf replacements, or modifications, generally require new structures.

Official driver education video -
https://www.youtube.com/watch?v=khFoQ-I ... qIXlK29v3i

On this layout diagram you can simultaneously see the old cloverleaf layout that's been replaced -
http://www.i-70projects.com/docs/I70T20 ... -03-14.pdf
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Re: Diverging Diamonds

Post by Bryn666 »

That would have far superior throughput because there isn't the stop start caused by continuous weaving.

Cloverleaves are terrible junctions these days.
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Al__S
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Re: Diverging Diamonds

Post by Al__S »

Peter Freeman wrote: Tue Feb 25, 2020 03:37

(a) it's changed from fully-free-flow on both crossing roads to non-free-flow on one of them, but has been deemed to work better anyway;
From that, it can be seen that the road that becomes non free-flow (SR19) has flat signalised junctions at the extent of the project, so free-flow at the junction with SR70 is not really of much use?
What it then does it takeaway the weaving in SR70- weaving is the major flaw of cloverleafs.
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Re: Diverging Diamonds

Post by Peter Freeman »

Al__S wrote: Tue Feb 25, 2020 06:42 From that, it can be seen that the road that becomes non free-flow (SR19) has flat signalised junctions at the extent of the project, so free-flow at the junction with SR70 is not really of much use?
What it then does it takeaway the weaving in SR70- weaving is the major flaw of cloverleafs.
Yes, although the blurb I've seen on it doesn't say which road was suffering congestion, presumably it was the I70, and this modification has removed the cause. The SR19 presumably could tolerate the previous weaving because its traffic volume was lower (many USA cloverleafs still work well enough, for this reason). And, as you point out, SR19 doesn't need to be free-flow since it has many other flat junctions, even nearby.

This unbalanced load situation might prevail at many troublesome cloverleafs, so perhaps the modify-to-a-DDI strategy will be applicable elsewhere.
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Re: Diverging Diamonds

Post by Chris5156 »

Peter Freeman wrote: Tue Feb 25, 2020 03:37 Most USA DDI's have been conversions from standard signalised diamonds, but I've just seen (what I think is) the first cloverleaf converted to a DDI. It is on the I70 in Pennsylvania. This is interesting because -

(a) it's changed from fully-free-flow on both crossing roads to non-free-flow on one of them, but has been deemed to work better anyway;

(b) cloverleaf replacements, or modifications, generally require new structures.
Really interesting. Even though no structure renewals are needed, it looks rather gold-plated to me, in that all four of the new junction's sliproads are being built from scratch, when a little bit of adjustment to curves would allow the original junction's right-turn slips to be retained. I don't know why you'd tear up a length of existing road to build a new length of the same standard right alongside it.
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