New Lower Thames Crossing

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Patrick Harper
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Re: New Lower Thames Crossing

Post by Patrick Harper »

If the aim of the non-motorway is for less PR backlash then I don't think they're fooling anyone.
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KeithW
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Re: New Lower Thames Crossing

Post by KeithW »

I dont see any sign of a PR backlash, probably because not only is the Dartford Crossing hopelessly overloaded but having a single point of failure on a major strategic route is a very bad idea. All you need is major collision involving a tanker on the A282 and you would have utter chaos.
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Re: New Lower Thames Crossing

Post by Bryn666 »

Patrick Harper wrote: Sat Jan 15, 2022 12:48 If the aim of the non-motorway is for less PR backlash then I don't think they're fooling anyone.
That's a bunch of antis desperate to can the scheme.

The LTC will be designed exactly like any other all purpose dual carriageway with 1m hard strips and full FSSD on the nearside verge so it will be nothing like a smart motorway purely because it is a new road and not a retrofitted one.
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Re: New Lower Thames Crossing

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FSSD?
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jackal
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Re: New Lower Thames Crossing

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A more substantial complaint could be with the proposed arrangement on the M25 southbound between J29 and the LTC, which bodges on a fifth lane with no HS, ALR style.

Northbound the current four lanes+discontinuous HS are retained, with the new capacity via a separate carriageway, which also prevents the spontaneous change in motorway regs seen southbound.

M25 J29 to LTC - Copy.JPG
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Re: New Lower Thames Crossing

Post by ABB125 »

I can't remember if this has been answered before, but why are they planning a separate carriageway northbound but not southbound?
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jackal
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Re: New Lower Thames Crossing

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Without the braiding and outercarriageway the weaving space would be tight northbound, due to the absolutely massive (and presumably NSL) fork.

M25 junction - Copy.JPG
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Re: New Lower Thames Crossing

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Herned wrote: Sun Jan 16, 2022 10:19FSSD?
Sorry, acronym wonkery alert - it's forward sight stopping distance. This determines design speed and is why so many new roads are 50 when FSSD requirements are gold plated along with curve radius requirements.

Smart motorways get a pass because they're retrofits.
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Re: New Lower Thames Crossing

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ABB125 wrote: Sun Jan 16, 2022 11:20 I can't remember if this has been answered before, but why are they planning a separate carriageway northbound but not southbound?
The fork is probably the main reason as Jackal says, but it might also be because less traffic will leave the M25 than join, due to the lopsided junction at the A13. As M25 clockwise to Tilbury is freeflow at the moment via J30 while the reverse requires the roundabout, a slip is provided to connect the A1089 to LTC northbound but the movements off the LTC to the A1089 is missing, with the existing route used. There must be a lot of traffic expected to be going to and from the port at Tilbury given the LTC southbound has been reduced to two lanes between the M25 and A13.

Further to that, while the LTC north to A1089 arrangement makes sense, why have they gone to considerable effort to include the circuitous and complicated A1089 to LTC southbound movement, but not provided the comparatively easy reverse movement?
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Re: New Lower Thames Crossing

Post by Steven »

Bryn666 wrote: Sun Jan 16, 2022 13:04
Herned wrote: Sun Jan 16, 2022 10:19FSSD?
Sorry, acronym wonkery alert - it's forward sight stopping distance. This determines design speed and is why so many new roads are 50 when FSSD requirements are gold plated along with curve radius requirements.

Smart motorways get a pass because they're retrofits.
Could you pop something about that on the Wiki please Bryn? I don't think that's an acronym that's explained on there.
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jackal
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Re: New Lower Thames Crossing

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Mapper89062 wrote: Sun Jan 16, 2022 16:28
ABB125 wrote: Sun Jan 16, 2022 11:20 I can't remember if this has been answered before, but why are they planning a separate carriageway northbound but not southbound?
The fork is probably the main reason as Jackal says, but it might also be because less traffic will leave the M25 than join, due to the lopsided junction at the A13. As M25 clockwise to Tilbury is freeflow at the moment via J30 while the reverse requires the roundabout, a slip is provided to connect the A1089 to LTC northbound but the movements off the LTC to the A1089 is missing, with the existing route used. There must be a lot of traffic expected to be going to and from the port at Tilbury given the LTC southbound has been reduced to two lanes between the M25 and A13.
While you're right that there's less turning traffic southbound, it's worth mentioning that volumes on the M25 will be the same in both directions north of the merge/diverge. So I guess the question is whether extra capacity is required where volumes are constant but turning percentage increases.
Further to that, while the LTC north to A1089 arrangement makes sense, why have they gone to considerable effort to include the circuitous and complicated A1089 to LTC southbound movement, but not provided the comparatively easy reverse movement?
There's also a separate scheme for Tilbury access, which I imagine will be a GSJ near the northern tunnel portal and link road, and which would seem to render the A1089 to LTC slip superfluous.

Also a bit weird that Orsett Cock to LTC is excluded when the reverse is provided.
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Gav
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Re: New Lower Thames Crossing

Post by Gav »

This will be a really unusual layout...

Looking at the M25 junction... w.ith the lower thames crossing...

You come along the road from the crossing and yo will have the option to head for the A127 junction on an a road or join the M25. the road will peel off and go to the a127 as an A road.. However to leave the A127 roundabout for the crossing you will have to join a motorway M25 before leaving... so in effect by default that road will only ever have motorway traffic on it till the A13
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Re: New Lower Thames Crossing

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"National Highways to reconsider Lower Thames Crossing use of ‘smart’ technology"

Seems to just be a clickbait headline as the nearest NH quotes are "[NH] will of course be reviewing the government’s announcement and considering any changes we may need to make" and "it is being designed to the highest standards recommended today, but we will continue to adapt our plans to incorporate advances in safety design and technology that will come forward in the years ahead."

But the logical endpoint of the "smart motorway by stealth" argument used by the Thames Crossing Action Group would indeed be to remove the smart technology, and just build it as a regular D3AP, like the nearby A13. That's undoubtedly worse for safety than a D3AP with the gadgets, but the NIMBYs and anti-smart motorway brigade don't care about such minor details.

https://www.newcivilengineer.com/latest ... 3-03-2022/
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Re: New Lower Thames Crossing

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jackal wrote: Thu Mar 03, 2022 15:57 "National Highways to reconsider Lower Thames Crossing use of ‘smart’ technology"

Seems to just be a clickbait headline as the nearest NH quotes are "[NH] will of course be reviewing the government’s announcement and considering any changes we may need to make" and "it is being designed to the highest standards recommended today, but we will continue to adapt our plans to incorporate advances in safety design and technology that will come forward in the years ahead."

But the logical endpoint of the "smart motorway by stealth" argument used by the Thames Crossing Action Group would indeed be to remove the smart technology, and just build it as a regular D3AP, like the nearby A13. That's undoubtedly worse for safety than a D3AP with the gadgets, but the NIMBYs and anti-smart motorway brigade don't care about such minor details.

https://www.newcivilengineer.com/latest ... 3-03-2022/
The NIMBYs will use this watering down as a reason to campaign against it for being 'unsafe'.

In all honesty, NH dropped a massive testicle by not just designing it as a conventional D3M motorway with passive provision for future ALR. Their fear of hard shoulders is just getting silly now.
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Re: New Lower Thames Crossing

Post by jackal »

Unfortunately not feasible for the tunnel. No TBM wide enough for four lanes has ever been constructed anywhere.

They could add HS to the surface route but it wouldn't be in the one place where you'd most want it, and would have no prospect of future ALR. Not great value really.
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Re: New Lower Thames Crossing

Post by jervi »

Might be an unpopular opinion, but why don't they construct it was a D2M (with an extra wide shoulder & ERAs), and then when traffic levels demand and safety concerns of no hard shoulder cease to exist, convert it to a D3ALR?
All that would be needing to be done when converting to ALR is the road markings, signs & a few AMIs added which would be a simple task if built to that design in the first place.

This has been done at the NorthConnex Tunnel in Sydney, AU which was recently built. It has been built as a D2M but wide enough for a D3 when they decided traffic levels meet levels of removing the shoulder.
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Re: New Lower Thames Crossing

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jackal wrote: Thu Mar 03, 2022 16:57 Unfortunately not feasible for the tunnel. No TBM wide enough for four lanes has ever been constructed anywhere.

They could add HS to the surface route but it wouldn't be in the one place where you'd most want it, and would have no prospect of future ALR. Not great value really.
Let's be realistic that the amount of supressed demand in Essex and Kent means a D3 tunnel will probably be inadequate before long anyway. The current Dartford Crossing takes over 130,000 vehicles and these are not all going to switch routes but I do expect a lot of trips people don't currently make will become extremely viable - if you live in Essex a job in Kent will suddenly be within much less stressful grasp.

If it gets built I give it until about 2045 before we're talking about adding a third tunnel here.
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Re: New Lower Thames Crossing

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A new consultation runs from Thursday, May 12, to Monday, June 20.

https://www.kentonline.co.uk/gravesend/ ... es-263980/
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Re: New Lower Thames Crossing

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jackal wrote: Sun Jan 16, 2022 17:00 There's also a separate scheme for Tilbury access, which I imagine will be a GSJ near the northern tunnel portal and link road, and which would seem to render the A1089 to LTC slip superfluous.
That junction just north of the river, serving Tilbury and a service area, is shown on one of the fly-throughs (perhaps I'm watching an out-of-date video?). Is that junction still planned? Guess what the GSJ type is - yes, a two-bridge roundabout!

I still think, having reminded myself of what's going on by a quick flick through this thread, that the LTC is being under-engineered in several ways -

1. I understand that there will be modifications to the J29 stackabout. I know that one mod is a 4th through-lane on the M25 :yes:. I presume left turn bypasses :thumbsup:. I suspect signalisation :thumbsdown:. I wonder whether any consideration was given to replacing it :shhh: ...?

2. I don't like any of the reductions to carriageway widths through junctions. I do understand 3+1=4, and other such simplistic lane sums. And I do understand that a lane drop can facilitate a subsequent lane gain. But skimping on width where merging or diverging is taking place is asking for trouble. Keep the width, get the diverging or merging done, then drop the surplus lane(s).

3. The braid at the fork northbound probably is required, but only (as already raised above) because of the loss of merging distance caused by that extravagent swooping curve. Otherwise, a reversal of the southbound (weaving) fork would suffice. The J29 noses are not actually that close to the LTC's. You just need to thin the lane occupancy down by having (more than) adequate width (and perhaps a 60mph limit, and J29 ramp metering :stir:).

4. I'm concerned by some very long single lane connectors. I actally like single lane ramps and connectors, when they match low volumes of traffic, but they shouldn't be too long. The problem that occurs is that platoons form, owing to slower vehicles developing tails. These platoons cause havoc as they all try to merge at once. The solution is for the connector to start as one lane, expand to two lanes in order to allow overtaking of the slow-coach, then compress to single lane once again for the merge.

5. Finally, the project is probably not quite ambitious enough. It will be overwhelmed in 20 years.

Apart from that lot, it's still a great project. Let's go, and cease all this shilly-shallying!
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Re: New Lower Thames Crossing

Post by WHBM »

jervi wrote: Thu Mar 03, 2022 17:21 Might be an unpopular opinion, but why don't they construct it was a D2M (with an extra wide shoulder & ERAs), and then when traffic levels demand and safety concerns of no hard shoulder cease to exist, convert it to a D3ALR?
Safety concerns are not the only thing about losing the hard shoulder. The disruption and delay caused by any breakdown, minor accident, or other event is a significant issue, as anyone listening to the London peak hour radio traffic reports can hear about the almost daily mention of the ALR sections of the M25 (not specifically announced as such, but apparent from the junction numbers), especially as an HGV tyre failure needs two lanes closed to change a wheel (in pre-ALR times it was left on the hard shoulder until after the peak period).

The construction of the two additional ERAs on the north side M25 caused about 18 months of comparable dislocation, especially as the two, about five miles apart, had a continuous lane 1 closure, including the intermediate ERA - and the actual construction works appeared to proceed at the speed of coastal erosion.
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