A57/A628 Mottram Tintwistle bypass

[Peter Freeman]

You are course free to believe I was in (c), for example if you think I should have declined the job and stayed on the dole queue.

Cheesecake Man: I have you safely in my category (a) .

[jackal]

There is a very real risk that removing the Mottram bottleneck whilst making lives immeasurably better for locals will just make Denton Island unbearable. It doesn't work now, and NH have tried nothing radical and are all out of ideas. Their last intervention, a free-flow left turn lane off the M60 anti-clockwise slammed traffic into a kerbed buildout and has achieved diddle squat. Something to help would be to utilise the missing flyover and provide some free-flow on/off the M60 - this helps strategic traffic whilst discouraging car commuting into the city centre.

I agree and made this more primitive drawing in 2016:

M60 J24 - Copy.png (3.61 KiB) Viewed 2115 times

Back to the current scheme, the Recommendation Report mentions that

Various IPs, including John Pasiecznik [REP2-077, REP4-023] and others have called for the provision of a long bypass, encompassing Hollingsworth and Tintwistle. Schemes to provide such a measure were considered during the development and optimisation of the Proposed Development, but not taken forward for the reasons outlined in ES Chapter 3 [REP2-036] and we are satisfied that the appraisal of alternative schemes was undertaken and has been sufficient to meet the requirements of the NPSNN (p. 63).

But when you look at the relevant ES chapter the "long bypass" was rejected because

the risk relating to funding for a long bypass being unavailable within the current RIS was highlighted. As a result, the decision was made to take the following the two [sic] Mottram Moor Link Road options (set out below) through to the next stage" (p. 113).

So the government/NH's argument against the long bypass is just that they chose the short one already...

Some of the options can be seen here, including the four options that made it to the "second sift" in January 2016: the Brown long bypass (same as the preferred route for the Mottram, Hollingworth and Tintwistle Bypass taken to Public Inquiry in 2007), the "DFT low cost option" long bypass (another historical option), and Mottram Moor Link Road options A and B (which were subsequently consulted on). Interestingly the Brown and DFT options would have gone opposite sides of Arnfield Reservoir.

[Peter Freeman]

There is a very real risk that removing the Mottram bottleneck whilst making lives immeasurably better for locals will just make Denton Island unbearable.

But if you fixed Denton Island too, some of your Glossop rail customers might defect to road! Seriously though, it does need fixing.

Something to help would be to utilise the missing flyover and provide some free-flow on/off the M60 - this helps strategic traffic whilst discouraging car commuting into the city centre.

That's quite good, and so is Jammy Dodge's variation. A trumpet's a good, classic motorway T-junction, and then the roundabout easily handles A57 traffic only. However, there are problems - such as that golf course, visual impact, high cost, constructability, and (perhaps) disruption to an important live traffic environment during construction.

I have a different and, I'm sure, controversial idea. It's one that won't surprise those who know my views. The solution to this problem is embedded in the location's name: Denton ISLAND. The elephant in the room is the roundabout. Bryn, you've fallen into the trap of following NH and DMRB's unwritten rule - "Every interchange must include at least one roundabout".

First, some observations from afar, gleaned through GM and GE:
1. Most wb M67 traffic turns onto M60 (nb and sb).
2. AM peak is the problem time, the PM peak less so.
3. The AM peak M67 queue is regularly 2km in length (GM 'typical traffic' shows red and maroon). One GE historical image shows a 3.5km queue there, with no sign of abnormal cause (accident, breakdown, etc) - and GE doesn't often catch a photo of the worst.
4. The PM peak A57 queue is typically 1km.
5. All left turns are handled well enough (though you may have to queue in order to reach them).
6. M60 mainline is congested at both peaks: sb only, hardly any nb.

Here's my solution: a powerful SPUI. It would fit in the space currently occupied by the roundabout, and, although you'll be sceptical, it would handle the flow required here. It would be relatively low cost and low disruption.

and provide some free-flow on/off the M60

Bryn, you've constrained the design process by pre-selecting one class of solution: free-flow. Instead, let's describe the problem first. What's missing here is turn capacity, not necessarily free-flow.

While you may think of a SPUI as a service interchange only, there are examples where the non-free-flow road is a pseudo-freeway. Although your instincts might reject signalisation of an M-to-M interchange, an open mind must agree that there is actually nothing wrong with it, if it performs as required.

A SPUI (aka Single Point Diamond) can have very high capacity. It is highly customisable via stop line widths. Although classically 3-stage, in practise they usually run 4 signal stages, in order to further accommodate on-ramp and thru-traffic a-symmetry. Four-stage operation (which I won't go into here) allows a 'semi-SPD' layout (where on-ramp tracks overlap), which is even more compact. All these features can be found in current implementations: 35 in AU, many more in USA and elsewhere.

Constructability and disruption will not be a problem. The process would be similar to that used at the M6J19 double-right-turn throughabout. All works would initially be inside the island, installing concrete planks to create a large platform over the motorway. The SPUI would be laid out on this platform, in a slightly shrunken form with temporary edging and signals, and commissioned. This temporary layout would be at least as competent as the current situation. After the interim commissioning, the curved bridges would be demolished, the platform enlarged, and the SPUI expanded to final form.

Demolition of the roundabout bridges would solve the side issue of M60 mainline congestion by allowing widening.

I anticipate a reaction of "surely this won't fit". It will. The Denton roundabout is ~135m diameter. Many UK roundabouts are really big, even bigger than this one (which makes them a strange choice for a country that worries about land-take). In contrast, you can measure almost any SPUI in Australia and find that the diagonal distance between left turn slips is less than 135m. This one in Melbourne would fit within Denton Island, and it's larger than the one I'm proposing. My SPUI would have 3-lane right turns between M60/M67, 2-lane right turns between M60/A57, 2-lane straights between M67/A57, and 1-lane or 2-lane left turns. It would have a semi-SPD configuration. Ramp metering and/or lane-gain at M60 merges is recommended.

I'd be interested to hear your views, whatever scepticism is included.

[Chris5156]

Denton Island is horribly constrained by the way the A56 and M67 are linked on the east side of the roundabout. Bryn/JammyDodge/Jackal's trumpet solutions are good (better than good, they're ingenious), but the weakness will be the conflict between left turns in and out of the M67 which have to weave through (or be signalised to cross over) traffic trying to get in and out of the A57. There's no easy fix for that.

The same issue would also affect any SPUI or similar plan. I have no ideological issue with that sort of thing, and have no great attachment to Denton Island as it stands, but having little experience of SPUIs in the wild I'd be interested to see an equivalent one in service. Traffic flows approaching from the east show about 50k AADT from the M67 and another 10k from the A57 - how many turning lanes are needed for a SPUI to handle 60k AADT on one of its signalised arms?

[Bryn666]

Peter has raised some great food for thought. Improving Denton needs to be mostly about improving usability and safety (capacity follows as a logical conclusion), whereas we tend to just consider capacity which results in virtually unusable and complex nonsense that confuses drivers no end. We tackle the wrong problem - just encouraging more driving on unsuitable and inadequate roads is madness; we have finite space, we should be making the strategic network as high quality as possible whilst discouraging solo occupancy cars clogging up approaches to cities. More park and rides, more options for commuting, more active travel. We just don't treat transport as a full picture and just go "dis good dat bad". Compare the UK to the Netherlands where in urban areas cycling has a massive share, but you can hop in your car and drive across the country into a park and ride without bother if a train can't do it for you.

I don't have an overarching issue to a SPUI or even a DDI - a SPUI is superior to a two bridge roundabout in so much that you have one set of signals as opposed to three to turn right. This could, possibly with a three lane movement, carry the turn flows needed.

The real issue is we don't build such junctions because "not invented here" - the only SPUI in the UK is in Belfast, which does its own thing anyway.

I may have to get my crayons out and see if a SPUI fits.

[Peter Freeman]

Thanks for the restrained and considered scepticism! Let me answer the easy part first.

Traffic flows approaching from the east show about 50k AADT from the M67 and another 10k from the A57 - how many turning lanes are needed for a SPUI to handle 60k AADT on one of its signalised arms?

Let's design for AM peak (all the rest will then be OK). The critical turn to get right is M67wb onto M60nb.

Let's aim for 60K pcu AADT approaching from M67 and assume that it splits equally between M60nb and M60sb. I'll ignore A57 straight-on for now.

The right turn through the SPUI onto M60nb therefore needs to accommodate 60K / 2 = 30K AADT.

30K AADT / 10 = 3K/hour (divide AADT by ten to calculate the weekday peak is a rule-of-thumb conversion to factor-in the 24x7 profile).

In my scheme, the signalling stage that includes the right turn phase onto M60nb would get 50% duty cycle at morning peak (my estimate - to be explained later). The right turn on-ramp, while flowing, would therefore need to accommodate 3K / 0.5 = 6K/hour.

Let's use 2K/hour/lane as saturation capacity. 6K / 2K = 3. In case there's too much optimism in the calculation, lets say 4. Hence my design would have 4 lanes for that turn.

This is a simplistic calculation, and would require proper modelling.

[Peter Freeman]

... but having little experience of SPUIs in the wild I'd be interested to see an equivalent one in service.

Yes, unfamiliar interchange types are hard to visualise when you don't have a chance to actually stand by the roadside and watch one in action, or to drive through. I had the same problem a few years ago before AU had any DDI's. I'd read much about them, and seen animations on YouTube, but in 2015 I decided to visit Kansas and Missouri (the home-base of USA DDI's) to see many examples for myself. It made all the difference - I was convinced.

YouTube has SPUI animations, which I'm sure you've seen, but you could also watch this video, which I've posted previously. It's not representative of what Denton Island would be like - in fact this is rather unusual - but it does show how pairs of flows are simultaneous, and it provides some sense of how efficiently and quickly traffic moves through a SPUI (careful though - some shots are speeded up!). The traffic in the video, BTW, is not particularly heavy.
https://www.youtube.com/watch?v=3fqsJkVLsg0&t=0s

I'm sure that after the first time you see a SPUI flowing, you'd be impressed and converted. They're magical.

[Peter Freeman]

Denton Island is horribly constrained by the way the A56 and M67 are linked on the east side of the roundabout. Bryn/JammyDodge/Jackal's trumpet solutions are good (better than good, they're ingenious), but the weakness will be the conflict between left turns in and out of the M67 which have to weave through (or be signalised to cross over) traffic trying to get in and out of the A57. There's no easy fix for that.

Those 'service road' connections just east of the roundabout could be designed around. There's a lot of unused space between the M67 carriageways there, left over from the M67-A57 flyover intention. That space makes not only the approach to a SPUI, with lengthy flaring for the L and R turns, but also the handling or diverting of those service roads, relatively easy. I don't see those details as problematic for either the SPUI or the trumpet solution.

[Peter Freeman]

I may have to get my crayons out and see if a SPUI fits.

Here's a comparison of Denton Island against an actual Melbourne SPUI, which is at the interchange of Toorak Road with M1 Monash Freeway. I opened two instances of google maps, exactly the same scale, lined the roads up, and then screenshot.

Now, this is not exactly the size of my Denton Island SPUI. Toorak Road is definitely not a motorway! However, M1 is D4. So it's near enough to make the point.

Look more closely here to see this one's lane configuration -
https://www.google.com.au/maps/@-37.844 ... a=!3m1!1e3

For Denton, one of the on-ramp right turns and one of the off-ramp right turns would need to be 3-lanes (possibly even 4-lane to M60nb) instead of the two shown here. The other two right turns would be 2-lane - same as here. The left turns (all free-flow except for pedestrian signals, where required) would need to be 2-lane or 3-lane connecting M60/M67, but only 1-lane connecting M60/A57 - same as here. So, in total, marginally more lanes for Denton than this one. On the other hand, employing a semi-SPD layout would reduce the platform size.

In short, the SPUI would fit easily.

[Bryn666]

I may have to get my crayons out and see if a SPUI fits.

Here's a comparison of Denton Island against an actual Melbourne SPUI, which is at the interchange of Toorak Road with M1 Monash Freeway. I opened two instances of google maps, exactly the same scale, lined the roads up, and then screenshot.


SPD-GSR comparison 3.jpg


Now, this is not exactly the size of my Denton Island SPUI. Toorak Road is definitely not a motorway! However, M1 is D4. So it's near enough to make the point.

Look more closely here to see this one's lane configuration -
https://www.google.com.au/maps/@-37.844 ... a=!3m1!1e3

For Denton, one of the on-ramp right turns and one of the off-ramp right turns would need to be 3-lanes (possibly even 4-lane to M60nb) instead of the two shown here. The other two right turns would be 2-lane - same as here. The left turns (all free-flow except for pedestrian signals, where required) would need to be 2-lane or 3-lane connecting M60/M67, but only 1-lane connecting M60/A57 - same as here. So, in total, marginally more lanes for Denton than this one. On the other hand, employing a semi-SPD layout would reduce the platform size.

In short, the SPUI would fit easily.

And having got the crayons out I can give you this.

[Hdeng16]

I take it the vehicle counts back up the assertion that m67-m60n is the dominant flow?

I always assumed most traffic using the woodhead/snake corridors would use the southern half of the M60 and anyone going north would go up to the M62.

And, as much as I’m not suggesting it’s the same thing, my experience of almost all of the M60 north-eastern quarter traffic light junctions are that they are all woefully underpowered

[Peter Freeman]

What a nice surprise to wake up to! That's a brilliant piece of work, Bryn.

Here are my comments. Virtually none is a criticism - just observations.

1. Your total size is slightly larger than I expected, but it fits, and matches up to existing paving, so it's OK. The staged construction might be slightly easier if it was a bit more compact, but the end result would not be as good.
2. Your design is British-looking to my eyes - which is good, because you're designing for Britain. The difference is in the greater degree of channelisation. This is a noticeable feature at many UK normal crossroads too, where the right-turn lanes are separated from straight-ons by a pedestrian refuge. There is a pedestrian safety advantage in that, especially for elders, disabled, etc. There's a safety advantage for drivers too, especially at an unfamiliar layout, and because they may stray from painted guidance lines. The disadvantage is 'waste-of-space', but we don't seem to be short of space here (I knew those giant roundabouts would come in handy one day !)
3. I like your usage of box-junction hatching. In AU we don't often use those.
4. I believe, on further thought, that the right turn from M67 to M60nb should have 4 lanes, in order to be sure about capacity. This of course subject to modelling at detailed design stage. If 4 lanes, I would suggest that it be channelised into 2x2. AU drivers cope perfectly well with side-by-side turning in 3 lanes, of which we have many, and I'm sure UK's would too. However, we don't AFAIK have any 4-lane turns, and they could be a bit hairy.
5. I like your handling of the service roads: signalised pretty much same as now.
6. Your inclusion of signals at the end of left-turn slips, where merging or give-way might be possible instead, is good. It's quite Australian actually - we don't seem to mind stopping or slowing down as much as UK drivers do.
7. I believe the left turns M60sb-to-M67 and M67-to-M60sb should have 3 lanes, to be sure of capacity. They only need to be flared for the 30m or so leading to the stop line.
8. With SPUI's, it's important that the flaring to right-turn stop-lines occurs early, because the signalling stages can be (and should be, for efficiency) quite long in duration. In this interchange type, there are no conflicts or blockings that artificially limit the duration - "let it bleed"! Your lengths look OK.
9. I like your extensions of the foot/cycle bridges. I wonder whether, for some people who tend to avoid pedestrian over-bridges and underpasses, there should be surace crossings too? (as there are in the current GSR layout).
10. You might like to try factoring in the semi-SPD aspect.

Now, you need to talk to the golf course people, just in case they will hand over some land for your trumpet instead.

[Bryn666]

I take it the vehicle counts back up the assertion that m67-m60n is the dominant flow?

I always assumed most traffic using the woodhead/snake corridors would use the southern half of the M60 and anyone going north would go up to the M62.

And, as much as I’m not suggesting it’s the same thing, my experience of almost all of the M60 north-eastern quarter traffic light junctions are that they are all woefully underpowered

It is a proof of concept rather than a "we must build this immediately". I rather expect the wonks who oversee this region's trunk roads would immediately dismiss it as "too complex", whereas somehow the existing pee poor incorrectly spiralled roundabout plus that lethal free-flow left turn slip into a build out are a-OK because DMRB says so. From experience turning left onto the M60 here is usually blocked by traffic wanting to turn right or go into Manchester. Splitting those flows out and having this layout removes a lot of that.

What a nice surprise to wake up to! That's a brilliant piece of work, Bryn.

Here are my comments. Virtually none is a criticism - just observations.

1. Your total size is slightly larger than I expected, but it fits, and matches up to existing paving, so it's OK. The staged construction might be slightly easier if it was a bit more compact, but the end result would not be as good.
2. Your design is British-looking to my eyes - which is good, because you're designing for Britain. The difference is in the greater degree of channelisation. This is a noticeable feature at many UK normal crossroads too, where the right-turn lanes are separated from straight-ons by a pedestrian refuge. There is a pedestrian safety advantage in that, especially for elders, disabled, etc. There's a safety advantage for drivers too, especially at an unfamiliar layout, and because they may stray from painted guidance lines. The disadvantage is 'waste-of-space', but we don't seem to be short of space here (I knew those giant roundabouts would come in handy one day !)
3. I like your usage of box-junction hatching. In AU we don't often use those.
4. I believe, on further thought, that the right turn from M67 to M60nb should have 4 lanes, in order to be sure about capacity. This of course subject to modelling at detailed design stage. If 4 lanes, I would suggest that it be channelised into 2x2. AU drivers cope perfectly well with side-by-side turning in 3 lanes, of which we have many, and I'm sure UK's would too. However, we don't AFAIK have any 4-lane turns, and they could be a bit hairy.
5. I like your handling of the service roads: signalised pretty much same as now.
6. Your inclusion of signals at the end of left-turn slips, where merging or give-way might be possible instead, is good. It's quite Australian actually - we don't seem to mind stopping or slowing down as much as UK drivers do.
7. I believe the left turns M60sb-to-M67 and M67-to-M60sb should have 3 lanes, to be sure of capacity. They only need to be flared for the 30m or so leading to the stop line.
8. With SPUI's, it's important that the flaring to right-turn stop-lines occurs early, because the signalling stages can be (and should be, for efficiency) quite long in duration. In this interchange type, there are no conflicts or blockings that artificially limit the duration - "let it bleed"! Your lengths look OK.
9. I like your extensions of the foot/cycle bridges. I wonder whether, for some people who tend to avoid pedestrian over-bridges and underpasses, there should be surace crossings too? (as there are in the current GSR layout).

Now, you need to talk to the golf course people, just in case they will hand over some land for your trumpet instead.

Thanks for the feedback - definitely one we could push as a concept, obviously subject to modelling and whatnot but if anyone seriously thinks the current roundabout is as good as it gets then I am calling them a liar right now. I reckon even a sub-optimal SPUI here would vastly outperform the roundabout.

I had considered at-grade crossings but took the view that this is a high capacity interchange and traffic could be moving at a fair lick (even 25-30mph can be daunting on foot) so went for the safer option of a bridge. I expect value engineering would bring back the at-grade crossings anyway, because who cares if pedestrians are stood waiting in the middle of a giant junction eh...

The trumpet might not be needed if all this was to work - it would be hard to build both for sure.

[Peter Freeman]

I take it the vehicle counts back up the assertion that m67-m60n is the dominant flow? I always assumed most traffic using the woodhead/snake corridors would use the southern half of the M60 and anyone going north would go up to the M62.

I haven't asserted a dominant flow. I've just assumed, as a convenience in my ignorance, an equal split. My concentration on M67-to-M60nb is because, out of the two heavy AM-peak flows, that's the one that, being a right turn, has a conflict that limits it's duration. Get that one right, and most of the rest falls into place.

[Hdeng16]

Fair enough guys - I honestly wasn’t looking for problems just questioning my own assumptions really.

[Peter Freeman]

Bryn, regarding the size of your SPUI, it looks to me that it could be built full size in one go, with the curved bridges still there. That is, omit my intermediate stage that uses a temporary smaller layout. Still probably knock the bridges down later, since there's no good way to either re-use them or to incorporate them.

I think the SPUI treatment (or your trumpet) would require M60 to be widened to D4ALR both north and south of Denton (initially only as far as the next junctions), since an unrestrained M67 will add a good lane-full of traffic. Therefore widening through this junction might not even be warranted.

[Bryn666]

Bryn, regarding the size of your SPUI, it looks to me that it could be built full size in one go, with the curved bridges still there. That is, omit my intermediate stage that uses a temporary smaller layout. Still probably knock the bridges down later, since there's no good way to either re-use them or to incorporate them.

I think the SPUI treatment (or your trumpet) would require M60 to be widened to D4ALR both north and south of Denton (initially only as far as the next junctions), since an unrestrained M67 will add a good lane-full of traffic. Therefore widening through this junction might not even be warranted.

North of J24 is already D4M up to J23, with a lane drop through there, then it's D4M up to J22 again so that's resolved easily! South would need to be ALR but that will cause issues at J25 which doesn't warrant a lane drop and there's no space to really widen through Stockport although if the A6 link road ever happens this is immediately fixed as a lot of traffic will head down the A555. There's a lot of local opposition to that road but the only way to fix the A6 through Hazel Grove is to remove it entirely and that means new bypass.

The existing bridges at J24 are weird as they are asymmetrical and allow 3+HS in one direction but not the other (it's 3 with no HS). With some tweaks you could easily fit a D4 ALR underneath even if it needs narrow lanes (not unheard of on the M60) but I doubt you'd need to. A full HS would be a good luxury though and worth having. The new super structure also should be capable of accepting SUDS planting along with all the verges and would not need to be acres of hard landscaping making this layout quite a big environmentally friendly alternative the concrete intensive roundabout.

99% of my unsure state about this junction has evaporated. I reckon this would probably be a decent fix on its own, it would certainly improve safety if nothing else (the existing roundabout has had issues).

[Bryn666]

Fair enough guys - I honestly wasn’t looking for problems just questioning my own assumptions really.

No, it's good to challenge ideas - far too much stuff gets to approval stage and no one has seemingly asked basics like "how does A N Pleb use this then"?

[Peter Freeman]

A few posts up-thread, Bryn mentioned a DDI for Denton Island. Needless to say, I'd thought about that before deciding to throw a SPUI into the ring first. They're my equal favourite 2-level service interchanges. They also occupied the top positions in a ranking table that Jackal produced for another topic.

AU has a DDI, and many SPUIs, that would fit at Denton. However, to make comparison easy, I've chosen a DDI and a SPUI that are close together, in Springfield, MO, USA. They both have the freeway on top, but that doesn't matter for size. You can easily scroll between the two on Google Maps, as they're just 3km apart on the same N-S freeway.

Here's the DDI -
https://www.google.com.au/maps/place/Sp ... 93.2922989

Here's the SPUI -
https://www.google.com.au/maps/place/Sp ... 93.2922989

Here's Denton Island -
https://www.google.com.au/maps/place/De ... -2.1354974

You'll see that they're all the same size as each other, and as the SPUI that Bryn has drawn for M60J24. The DDI and the SPUI would both work, both could have the capacity, and both would fit. The DDI might be cheaper. Food for thought.

(edit: Open the three links simultaneously into three separate windows, and don't zoom. You'll see that the scale is similar on each image, and each interchange is identical in its footprint/land-take.).

[Bryn666]

A few posts up-thread, Bryn mentioned a DDI for Denton Island. Needless to say, I'd thought about that before deciding to throw a SPUI into the ring first. They're my equal favourite 2-level service interchanges. They also occupied the top positions in a ranking table that Jackal produced for another topic.

AU has a DDI that would fit at Denton. However, to make comparison easy, I've chosen a DDI and a SPUI that are close together, in Springfield, MO, USA. They both have the freeway on top, but that doesn't matter for size. You can easily scroll between the two on Google Maps, as they're just 3km apart on the same N-S freeway.

Here's the DDI -
https://www.google.com.au/maps/place/Sp ... 93.2922989

Here's the SPUI -
https://www.google.com.au/maps/place/Sp ... 93.2922989

Here's Denton Island -
https://www.google.com.au/maps/place/De ... -2.1354974

You'll see that they're all the same size as each other, and as the SPUI that Bryn has drawn for M60J24. The DDI and the SPUI would both work, both could have the capacity, and both would fit. The DDI might be cheaper. Food for thought.

Personally I'd rather trial the DDI at J7 instead where the A56 crosses over because this has huge active travel potential for a corridor that desperately needs it. I even did a video on my YT channel about that one: https://www.youtube.com/watch?v=dFlMjATjNG4

The M60 needs several interventions to improve crossing and getting on and off it, and as I've said before, NH have tried nothing radical and are all out of ideas.

Imagine the fundamental change we could bring if J24 was done as the SPUI and J7 as a DDI. We might actually become a forward thinking highway engineering nation not still reliant on roundabouts for everything.