Diverging Diamonds

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Peter Freeman
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Re: Diverging Diamonds

Post by Peter Freeman »

jackal wrote: Tue Jul 19, 2022 00:06 We have some quite bad cases in the UK of wrong side merges and diverges, and while more lanes helps in some respects, it doesn't in others. For instance, adding lanes to the M25 anticlockwise through Chevening with a wider approach would mean that trucks heading for the A21 would have to move across several lanes to get to their exit, disrupting the M25 flow. I'm not fanatically anti-offside exits, but a nearside exit for a much lower volume route is inherently better in my view as it keeps slow traffic out of fast lanes.
I'm ashamed to say that Chevening once caught me out, long ago, when travelling anticlockwise. Looking at the signage now on streetview, it's actually clear enough. A more graphic additional illustration of the layout would help further.

The problem of finding oneself in slow traffic on the right side of the carriageway is real, but in the case of Chevening there's quite a distance to achieve two or three lane hops before the next exit, especially when travelling clockwise.

As I've often remarked in other contexts, I suppose AU's and USA's laissez-faire lane discipline reduces this problem. (Note, I don't hold AU's approach to lane selection either better or worse than the UK's stricter interpretation - just different. They both work, as long as you know what's expected. And here in AU we do have occasional advisory signs reading "keep left unless overtaking").
Last edited by Peter Freeman on Wed Jul 20, 2022 10:25, edited 1 time in total.
Peter Freeman
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Re: Diverging Diamonds

Post by Peter Freeman »

Gav wrote: Tue Jul 19, 2022 21:27 I wonder if a diverging diamond could be done at hermistongait and then that would ease the congestion.
In my opinion, a DDI would ease the congestion at any signalised 4-arm roundabout, as long as it could be fitted in (and generally, it could be, as it's inherently more compact). However, Hermiston Gait's existing structures and surrounds are rather complicated and would need some careful thought.
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Chris5156
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Re: Diverging Diamonds

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Peter Freeman wrote: Wed Jul 20, 2022 10:07
jackal wrote: Tue Jul 19, 2022 00:06We have some quite bad cases in the UK of wrong side merges and diverges, and while more lanes helps in some respects, it doesn't in others. For instance, adding lanes to the M25 anticlockwise through Chevening with a wider approach would mean that trucks heading for the A21 would have to move across several lanes to get to their exit, disrupting the M25 flow. I'm not fanatically anti-offside exits, but a nearside exit for a much lower volume route is inherently better in my view as it keeps slow traffic out of fast lanes.
I'm ashamed to say that Chevening once caught me out, long ago, when travelling anticlockwise. Looking at the signage now on streetview, it's actually clear enough. A more graphic additional illustration of the layout would help further.

The problem of finding oneself in slow traffic on the right side of the carriageway is real, but in the case of Chevening there's quite a distance to achieve two or three lane hops before the next exit, especially when travelling clockwise.

As I've often remarked in other contexts, I suppose AU's and USA's laissez-faire lane discipline reduces this problem. (Note, I don't hold AU's approach to lane selection either better or worse than the UK's stricter interpretation - just different. They both work, as long as you know what's expected. And here in AU we do have occasional advisory signs reading "keep left unless overtaking").
I think the issue is not just about the overtaking rule, but also speed differentials between vehicles. Larger vehicles have lower speed limits, so a big truck that is mechanically limited to 56mph will have a hard time moving into lane 3 for an exit. Its presence over on the "fast" side of the road will also slow down other traffic and present a hazard, and potentially reduce capacity marginally. For that reason it's very desirable to keep exits on the left.
Peter Freeman
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Re: Diverging Diamonds

Post by Peter Freeman »

Chris5156 wrote: Wed Jul 20, 2022 12:27 ... For that reason it's very desirable to keep exits on the left.
Agreed - in general. However, I think there's room for many exceptions.

In particular, (a) where no other junctions are close enough to inhibit early occupation of a preferred lane, and (b) where leaving and continuing flows are not greatly unbalanced. I wonder whether situation (b) is the case at Chevening. Looking at Google Maps' 'typical' displays, this SE corner of the M25 seems to be its quietest part, and the junction appears not to cause major congestion despite the TOTSOs.

Regarding the contrast with Australia, we not only have a different overtaking/undertaking culture, but speed differentials between vehicle classes are less pronounced. Our trucks easily reach the speed limits (which are often lower than the UK's, on our mostly-urban motorways), and limits are strictly enforced.
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Gav
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Re: Diverging Diamonds

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Peter Freeman wrote: Wed Jul 20, 2022 10:22
Gav wrote: Tue Jul 19, 2022 21:27 I wonder if a diverging diamond could be done at hermistongait and then that would ease the congestion.
In my opinion, a DDI would ease the congestion at any signalised 4-arm roundabout, as long as it could be fitted in (and generally, it could be, as it's inherently more compact). However, Hermiston Gait's existing structures and surrounds are rather complicated and would need some careful thought.
looking at it and the main traffic flows it could be done quite easily, and it would increase the flow a fair bit. most of the conflicts would then be drawn to one main 'x' where the M8 comes in and swaps sides...
Peter Freeman
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Re: Diverging Diamonds

Post by Peter Freeman »

Gav wrote: Thu Aug 04, 2022 20:01
Peter Freeman wrote: Wed Jul 20, 2022 10:22
Gav wrote: Tue Jul 19, 2022 21:27 I wonder if a diverging diamond could be done at hermistongait and then that would ease the congestion.
In my opinion, a DDI would ease the congestion at any signalised 4-arm roundabout, as long as it could be fitted in (and generally, it could be, as it's inherently more compact). However, Hermiston Gait's existing structures and surrounds are rather complicated and would need some careful thought.
looking at it and the main traffic flows it could be done quite easily, and it would increase the flow a fair bit. most of the conflicts would then be drawn to one main 'x' where the M8 comes in and swaps sides...
I have no familiarity with this interchange, but having now taken another look via GM and GE, I despair at how such a layout could have arisen. I'd like to say it's the result of incrementally adding bits-n-pieces to fix up unanticipated problems, which is the excuse at many locations (Switch Island, M1J24, ...). However, GE historical view shows that it's always had this ridiculous form.

GM traffic layer (typical) shows moderate peak congestion, so it could do with some help, but a DDI is inappropriate here. It needs freeflow, but not in the current form. Two other embarrassingly-nearby, and also inappropriate, elevated roundabout interchanges on the A720 complicate the design problem.

I'm surprised that a Sabre search doesn't show up more discussion of this location, or any viable re-designs by Sabristi. The following topics do show up -
viewtopic.php?p=689626&hilit=hermiston#p689626
viewtopic.php?p=599594&hilit=hermiston#p599594
Peter Freeman
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Re: Diverging Diamonds

Post by Peter Freeman »

Australia's 7th DDI will replace a standard signalised diamond at the interchange of Picton Road B88 and Hume Motorway M31 in NSW. Consultations and detailed design are underway, but construction has not yet been funded or scheduled. I estimate a start in 2025 or 2026.
Project page -
https://roads-waterways.transport.nsw.g ... index.html
Last edited by Peter Freeman on Thu Nov 24, 2022 01:11, edited 1 time in total.
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ChrisH
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Re: Diverging Diamonds

Post by ChrisH »

Italy sees the diverging diamond and raises you... a diverging cloverleaf.

Looks like it has been installed not to interfere with the toll booth on the A4.
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Re: Diverging Diamonds

Post by Peter Freeman »

ChrisH wrote: Wed Nov 23, 2022 15:33 Italy sees the diverging diamond and raises you... a diverging cloverleaf.

Looks like it has been installed not to interfere with the toll booth on the A4.
Fascinating! ... as are many other complex interchanges in that vicinity.

Yes, the pre-existing A4 toll plaza was presumably the reason for the divergence; and then, given the divergence, the cloverleaf loops were positioned internally, to avoid them sticking out a long way E and W; and then, the crossing-over is there in order to keep the on- and off-ramps on the correct side (right in Italy).

As an alternative, the A50 could perhaps have crossed the A4 much more simply if routed slightly east or west, thus avoiding the plaza, but then it would not have captured A4 tolls in both directions from interchanging traffic.

That vast toll plaza, and various others nearby, is also 'impressive', but surely years out of fashion. In Australia, by 2000, we had moved to non-stop high-speed electronic tolling, which saves space, construction cost, journey delays, etc. Our system used, initially, Spanish technology. You would think that Italy, then but especially now, would have modernised by collaborating with its nearby Latin neighbour.
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Re: Diverging Diamonds

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Peter Freeman wrote: Thu Nov 24, 2022 01:24That vast toll plaza, and various others nearby, is also 'impressive', but surely years out of fashion. In Australia, by 2000, we had moved to non-stop high-speed electronic tolling, which saves space, construction cost, journey delays, etc. Our system used, initially, Spanish technology. You would think that Italy, then but especially now, would have modernised by collaborating with its nearby Latin neighbour.
Italy evidently doesn’t consider it a priority, and unlike Australia has many hundreds - indeed, probably thousands - of toll plazas that would all require conversion in a rapid time frame. Spain is the same, as are France and other nations with extensive tolled networks. I expect one reason Australia could be an early adopter and a completist is that, by comparison, the job was very small.
Peter Freeman
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Re: Diverging Diamonds

Post by Peter Freeman »

^ Yes, you're right: a large job for them, and there's not much incentive. However, I don't see a problem with converting one-by-one.
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Re: Diverging Diamonds

Post by Vierwielen »

Peter Freeman wrote: Thu Nov 24, 2022 01:24
ChrisH wrote: Wed Nov 23, 2022 15:33 Italy sees the diverging diamond and raises you... a diverging cloverleaf.

Looks like it has been installed not to interfere with the toll booth on the A4.
Fascinating! ... as are many other complex interchanges in that vicinity.

Yes, the pre-existing A4 toll plaza was presumably the reason for the divergence; and then, given the divergence, the cloverleaf loops were positioned internally, to avoid them sticking out a long way E and W; and then, the crossing-over is there in order to keep the on- and off-ramps on the correct side (right in Italy).

As an alternative, the A50 could perhaps have crossed the A4 much more simply if routed slightly east or west, thus avoiding the plaza, but then it would not have captured A4 tolls in both directions from interchanging traffic.

That vast toll plaza, and various others nearby, is also 'impressive', but surely years out of fashion. In Australia, by 2000, we had moved to non-stop high-speed electronic tolling, which saves space, construction cost, journey delays, etc. Our system used, initially, Spanish technology. You would think that Italy, then but especially now, would have modernised by collaborating with its nearby Latin neighbour.
I worked in Italy in 2001/2. At that time, the Telepass was quite common, a transponder that you carried in your car which woudl automatically open the gate. Provided that you have enough gates, it done not slow you down much. Also, unlike Australia, Italy has to accomodate foreign visitors who bring their own car.
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Re: Diverging Diamonds

Post by Bryn666 »

Peter Freeman wrote: Thu Nov 24, 2022 12:02 ^ Yes, you're right: a large job for them, and there's not much incentive. However, I don't see a problem with converting one-by-one.
France is working towards this aim - indeed the new A79 opened this year is the first all télepéage/number plate read only autoroute.
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Re: Diverging Diamonds

Post by emmatownson »

Hi all,

I am currently in the final year of my MEng Civil and Structural Engineering degree at The University Of Sheffield and am undertaking my dissertation on Diverging Diamond Interchanges (DDI), supported by Arup.

Within this research, I am aiming to survey 100 members of the public, of any background or age, regarding their opinion about DDI installation within the UK highways network and the perceived safety of this new interchange. You do not need to have any prior knowledge regarding DDIs or have an engineering background to complete this survey.

More information regarding my research can be found within the participant information sheet linked at the start of the survey.

Please can you share this with any family, friends, housemates, work colleagues etc - it is quite a tight turnaround as the survey closes on Wednesday 10th May!

I would appreciate any responses to the survey, the link is below (it may need to be copied and pasted into a new browser): https://forms.gle/1Fudib9JwHaPntG97

Thank you! :)
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Bryn666
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Re: Diverging Diamonds

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emmatownson wrote: Thu Apr 27, 2023 11:03 Hi all,

I am currently in the final year of my MEng Civil and Structural Engineering degree at The University Of Sheffield and am undertaking my dissertation on Diverging Diamond Interchanges (DDI), supported by Arup.

Within this research, I am aiming to survey 100 members of the public, of any background or age, regarding their opinion about DDI installation within the UK highways network and the perceived safety of this new interchange. You do not need to have any prior knowledge regarding DDIs or have an engineering background to complete this survey.

More information regarding my research can be found within the participant information sheet linked at the start of the survey.

Please can you share this with any family, friends, housemates, work colleagues etc - it is quite a tight turnaround as the survey closes on Wednesday 10th May!

I would appreciate any responses to the survey, the link is below (it may need to be copied and pasted into a new browser): https://forms.gle/1Fudib9JwHaPntG97

Thank you! :)
I have filled in the survey - I am quite a big advocate for DDIs in the UK, indeed the illustration you have in your survey is the one I drew up for a Twitter post about them - and for me the ideal trial site in the UK is M60 Junction 7, which I did a brief YouTube video about here: https://www.youtube.com/watch?v=dFlMjATjNG4
Bryn
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Vierwielen
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Re: Diverging Diamonds

Post by Vierwielen »

emmatownson wrote: Thu Apr 27, 2023 11:03 Hi all,

I am currently in the final year of my MEng Civil and Structural Engineering degree at The University Of Sheffield and am undertaking my dissertation on Diverging Diamond Interchanges (DDI), supported by Arup.

Within this research, I am aiming to survey 100 members of the public, of any background or age, regarding their opinion about DDI installation within the UK highways network and the perceived safety of this new interchange. You do not need to have any prior knowledge regarding DDIs or have an engineering background to complete this survey.

More information regarding my research can be found within the participant information sheet linked at the start of the survey.

Please can you share this with any family, friends, housemates, work colleagues etc - it is quite a tight turnaround as the survey closes on Wednesday 10th May!

I would appreciate any responses to the survey, the link is below (it may need to be copied and pasted into a new browser): https://forms.gle/1Fudib9JwHaPntG97

Thank you! :)
Hi emmatownson,

I have completed your survey. May I make one suggestion - add a note that if the person filling in the questinaire is retired, hten they should fill in their work status immediately before they retired.
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Re: Diverging Diamonds

Post by emmatownson »

Hi Both,

I apologise for the slow reply. Thank you for completing my survey.

Bryn666 I have come across your video during my research! I am hoping to suggest a location for a potential DDI pilot so will look into the M6- J7 thank you.

Vierwielen thank you for your suggestion, unfortunately, I am unable to change the survey as it would need to go through the ethical procedure again, however, for any further surveys I do on this topic or outside I will make sure I do so.

Also sorry if I have not replied in the correct way!
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Re: Diverging Diamonds

Post by Vierwielen »

emmatownson wrote: Sat May 06, 2023 16:22 Hi Both,

I apologise for the slow reply. Thank you for completing my survey.

Bryn666 I have come across your video during my research! I am hoping to suggest a location for a potential DDI pilot so will look into the M6- J7 thank you.

Vierwielen thank you for your suggestion, unfortunately, I am unable to change the survey as it would need to go through the ethical procedure again, however, for any further surveys I do on this topic or outside I will make sure I do so.

Also sorry if I have not replied in the correct way!
Hi emmatownson,
Even if you cannot change the questions that you used, it might be possble for you to note that this shortcoming was identified by a respondent and that one of your recommendations is that the university guidance for suverys such as this one be updated to reflect this condition. Of course, in some surveys, "retired" is more important than one's job before one retired - for example, in a social sciences survey "What is your household income"? the status of "retired" is very important.
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Vierwielen
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Re: Diverging Diamonds

Post by Vierwielen »

Vierwielen wrote: Wed May 10, 2023 22:28
emmatownson wrote: Sat May 06, 2023 16:22 Hi Both,

I apologise for the slow reply. Thank you for completing my survey.

Bryn666 I have come across your video during my research! I am hoping to suggest a location for a potential DDI pilot so will look into the M6- J7 thank you.

Vierwielen thank you for your suggestion, unfortunately, I am unable to change the survey as it would need to go through the ethical procedure again, however, for any further surveys I do on this topic or outside I will make sure I do so.

Also sorry if I have not replied in the correct way!
Hi emmatownson,
Even if you cannot change the questions that you used, it might be possble for you to note that this shortcoming was identified by a respondent and that one of your recommendations is that the university guidance for suverys such as this one be updated to reflect this condition. Of course, in some surveys, "retired" is more important than one's job before one retired - for example, in a social sciences survey "What is your household income"? the status of "retired" is very important.
To put this into perspective, I am retired and in comparison to when I was working, my income is low, but then my children are off my hands, my mortgage is paid off and I am drawing from my pension rather than contributing to it. However, many of my views are still influenced by my professional experience.
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jackal
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Re: Diverging Diamonds

Post by jackal »

Debaser wrote: Sun Oct 24, 2021 12:20
ABB125 wrote: Sun Oct 24, 2021 12:08 Is the WSP report available to read?
See Figure 1-4 of this report. https://www.sthelens.gov.uk/media/33176 ... ptions.pdf
The link has changed to this: https://www.sthelens.gov.uk/media/2091/ ... 7387470000

And here's the DDI in all its glory:

M6 J23 - Copy.JPG
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