New Lower Thames Crossing

[Chris5156]

As discussed previously, very wide carriageways have a bad rep in the UK because they tend to be used in locations with tight junction spacing. They should cope better on a longer stretch like this.

Many of DMRB's odd rules about not doing things that appear to be done safely and commonly around the rest of the world seem to come down to this sort of thing - we tried it in the wrong situation and it went badly.

It's a bit like refusing to have a kettle in your house because that one time you borrowed your neighbour's kettle to heat up some chunky vegetable soup it was impossible to clean afterwards.

[ManomayLR]

As discussed previously, very wide carriageways have a bad rep in the UK because they tend to be used in locations with tight junction spacing. They should cope better on a longer stretch like this.

Many of DMRB's odd rules about not doing things that appear to be done safely and commonly around the rest of the world seem to come down to this sort of thing - we tried it in the wrong situation and it went badly.

It's a bit like refusing to have a kettle in your house because that one time you borrowed your neighbour's kettle to heat up some chunky vegetable soup it was impossible to clean afterwards.

In our school the design and tech teachers also teach food tech (glorified cooking classes).
I spoke to one of them last year and she said she had seen year 7s pour couscous and stock cubes directly into the kettle.

Thank goodness for ready meals.

[Keiji]

Am I missing something, or could they just add in a sliproad as highlighted here in green?

The minimum space between successive diverges is 3.75V m, where V is design speed of the link. 3.75*85=318.75m, whereas your green slip has about 50m Alas, it's not easy to design a complex DMRB-compliant interchange - which is why I give the designers here credit for managing as much as they have.

Other than "it's not DMRB-compliant", what's wrong with having diverges arbitrarily close to each other, or happening at the same time? The lanes would be clearly indicated on an advance gantry, so who cares when one peels off relative to another?

Sounds like this rule about diverge spacing falls into the same category as the rule about wide carriageways that's been mentioned since...

[ABB125]

Am I missing something, or could they just add in a sliproad as highlighted here in green?

The minimum space between successive diverges is 3.75V m, where V is design speed of the link. 3.75*85=318.75m, whereas your green slip has about 50m Alas, it's not easy to design a complex DMRB-compliant interchange - which is why I give the designers here credit for managing as much as they have.

Other than "it's not DMRB-compliant", what's wrong with having diverges arbitrarily close to each other, or happening at the same time? The lanes would be clearly indicated on an advance gantry, so who cares when one peels off relative to another?

Sounds like this rule about diverge spacing falls into the same category as the rule about wide carriageways that's been mentioned since...

I can understand how very closely-spaced diverges may cause "driver confusion", but there's nothing wrong with a 3-way split in my opinion (as long as it's adequately signed!), assuming that it entirely uses lane drops (because anything else would probably become a confusing mess of paint). Possibly something like this:

...\\...||...//
.....\\ || //
.....||||||
......\\||||
.......\||||
........||||

[Bryn666]

Am I missing something, or could they just add in a sliproad as highlighted here in green?

The minimum space between successive diverges is 3.75V m, where V is design speed of the link. 3.75*85=318.75m, whereas your green slip has about 50m Alas, it's not easy to design a complex DMRB-compliant interchange - which is why I give the designers here credit for managing as much as they have.

Other than "it's not DMRB-compliant", what's wrong with having diverges arbitrarily close to each other, or happening at the same time? The lanes would be clearly indicated on an advance gantry, so who cares when one peels off relative to another?

Sounds like this rule about diverge spacing falls into the same category as the rule about wide carriageways that's been mentioned since...

The theory is it is confusing to drivers, but that's because we have never designed adequate overhead signage that can show multiple exits in rapid succession. How does the rest of the world cope???

[Mapper89062]

I assume that M25 clockwise to Tilbury is still going to be signposted via the free flow M25/A13 route rather than down the LTC and through the circuitous Orsett Cock U-turn? If so then providing the movement like this rather than more directly makes sense actually, since it avoids the need to revert the northern part of the LTC to D3 southbound while still having the route provided via the LTC as a backup when necessary. (Ideally there could be light-up signage on the M25 before the LTC exit that says something like 'Congestion on M25/A13 ahead, use A122 for Tilbury' when necessary, which I should probably suggest in my consultation response.)

Similarly, the Tilbury link clearly renders LTC NB -> A1089 redundant, so maybe the route for that movement at Orsett is an intentionally convoluted route to encourage people to divert to the Tilbury link if it opens, while still having the option there for resiliency?

I'm very impressed by the way they keep adding more and more spaghetti to that junction though , and sacrificing one minor freeflow movement probably is worth the extra movements.

[jackal]

There are some nice flow diagrams in the 2018 Traffic Forecasting Report, which shed light on some of the design decisions. For instance, A13wb to A1089 is a minor movement, hence it has lost freeflow in the latest iteration to make space for additional movements. You can also see that A1089 to LTCnb is a heavy movement, explaining why LTCnb has an extra lane than LTCsb in the current version.

[Peter Freeman]

^ Well, someone certainly did their homework for those diagrams! Without being able to fully justify this statement, and without trying to come up with better, I still have the nagging feeling that this junction (LTC/A13/A1089), and perhaps even the M2 junction, needn't have ended up so spaghetti-ish ...

[Herned]

^ Well, someone certainly did their homework for those diagrams! Without being able to fully justify this statement, and without trying to come up with better, I still have the nagging feeling that this junction (LTC/A13/A1089), and perhaps even the M2 junction, needn't have ended up so spaghetti-ish ...

That's not a complaint I would ever expect to hear on this site!

For once HE are building something which seems entirely fit for purpose (ignoring the bizarre choice to not make it a motorway)

[Peter Freeman]

^ It wasn't intended as a complaint - just a quiet reflection. Your congratulation of HE (NH) is correct.

[jackal]

I agree they've done a good job, but my lingering concern is that too much is going through Orsett Cock. It already has two A roads to handle, it doesn't need a load of 'missing' movements (five of them) from the LTC/A13/A1089 interchange on top of that.

I've made a sketch of my U-turn idea, which would address this issue. The following movements which have to do a full circuit of Orsett Cock under NH's plans can instead use the freeflow U-turn facility:

LTCsb to A1089
LTCsb to A13wb
LTCnb to A1089
LTCnb to A13wb

As well as adding a new bridge across the A13 for the U-turn I've reconfigured the braiding between the A13eb offslip and the onslip from the LTC. This is so the slip from the LTC is on the right hand side approaching Orsett Cock roundabout, where it can access the U-turn. The A13eb offslip is on the left as it does not need to access the U-turn (A13eb has direct access to the A1089). The A13sb offslip and the LTC slip enter the signalised Orsett Cock roundabout adjacent to each other.

(Click to expand.)

With the U-turn facility in place, I believe the only movement 'missing' from the LTC/A13/A1089 interchange that is catered for at Orsett Cock is A13wb to A1089 - a lot better than handling five missing movements.

EDIT: A version of the U-turn without the reconfigured braiding. This is a less complicated change to the NH proposal, but is less good as the U-turn traffic would have to be signalised

[AnOrdinarySABREUser]

I'm a bit surprised that there hasn't been much mention of how the Lower Thames Crossing is supposed to alleviate traffic at the Dartford Crossing, which to my knowledge was the original aim of the scheme? While the LTC does definitely fulfill the purpose of a strategic corridor, it is simply not fit for purpose. Not only has it been proved in the past that new roads, especially with the aim of alleviating traffic were not successful in that regard and usually contributed to more congestion on both roads, and I wouldn't be surprised if the LTC in it's current form is no different, without mentioning the environmental issues it'll cause especially since it goes over woodland, a SSSI and partly intrudes into the Kent Downs AONB!

I think a better solution would be a new High Speed line to the north branching off of HS1, since freight trains are more efficient in carrying cargo than lorries. There could be links between HS2 and this proposed High Speed line but I doubt it'll be necessary considering that HS2 to be knowledge will link up with HS1 already.

However, if we were still laser focused on providing a new road crossing, I would say that a now forgotten option, Option A14 (as a part of the options under, well, Option A) could be a better route than the one National Highways is currently opting for, since it doesn't intrude on any AONBs and such and only goes through the Green Belt. It would have bypassed the A282 and Dartford Crossing in it's entirety in a bored tunnel, coming out just south of Darenth and emerging just after Mardyke, both at fork junctions, with maps of the layout attached below, alongside an alternate configuration of the fork below Darenth so that freight traffic doesn't have to move to the right.




That being said, it would likely be quite expensive if not more expensive than Option C4, however here's the real kicker: there would be little intrusion on green belt with this forgotten option and no AONB or SSSI land would be cleared for the LTC, local traffic could use the existing Dartford Crossing with bus lanes perhaps being allocated, and would allow for the M25 for finally become the orbital motorway it has longed to be! Not even that, a comparison of the impacts both options would have in regards to Option C4 (the current option) and Option A14.



So, I have attached another image of where traffic currently goes, and comparing Option A14 to the current route chosen for the LTC, Option A14, at least in my opinion, would be far more effective at enabling flow for national traffic as well as providing the existing Dartford Crossing as a way for local and regional traffic to access those areas. Therefore, the LTC in it's current form only caters to some of the traffic that uses the Dartford Crossing, and from the looks it is Cross-Channel/Kent traffic heading up north to Essex and vice versa, so it wouldn't particularly help out in relieving the current Dartford Crossing, would just increase congestion and pollution, and has poor local/regional access, especially considering that National Highways has omitted junctions serving local traffic in Gravesend and Tilbury.



Also, the entirety of Option A14 being in a tunnel apart from when it emerges from the fork junctions would be extremely beneficial to the environment as greenhouse gas emissions can be filtered out, further reducing the impact this would have on the atmosphere. Oh, and did I mention that Option A14 could see a potential 40% reduction in traffic compared to the current proposed route of the LTC's 12%? Oh, and not to mention that Dartford and any area in the vicinity of the Dartford Crossing are facing very high levels of pollution, in fact high enough to exceed the WHO's legal limit of some greenhouse gases, like PM2.5, a substance which can cause lung problems and deadly heart attacks.

TL;DR: The current LTC is inadequate and will actually cause greenhouse gas emissions to rise in the area and will likely worsen the congestion and do little to nothing to mitigate the traffic on the existing Dartford Crossing. It will also cause a spew of environmental issues (encroaching upon Kent Downs AONB and a SSSI) and will continue to worsen pollution in the vicinity of the proposed route, the A2 and the Dartford Crossing. In comparison, Option A14 offers to reduce congestion by 40% and decrease emissions by a proposed 600,000+ tons.

Keep in mind this is only my opinion based off of the statistics and data available to me, and I will be happy to provide sources if anyone would like to do further reading on this.

[jackal]

The application has been resubmitted to the Planning Inspectorate:

https://infrastructure.planninginspecto ... -crossing/#

[Peter Freeman]

... I would say that a now forgotten option, Option A14 (as a part of the options under, well, Option A) could be a better route than the one National Highways is currently opting for, ...

I think your analysis may be correct if the focus is only on alleviating congestion on, and around, the bridge. That option simply adds express lanes that bypass the bridge and three busy junctions. Despite the longer tunnels, using TBMs, it would turn out to be lower in both cost and all adverse impacts.

However, the NH proposal partially unloads the Dartford crossing and then does more. It's a short-cut for N-SE traffic, and provides bonus local connections. Now-deleted local connections (eg. Tilbury) north of the river would have further exploited this tunnel, at relatively low cost.

[Bryn666]

... I would say that a now forgotten option, Option A14 (as a part of the options under, well, Option A) could be a better route than the one National Highways is currently opting for, ...

I think your analysis may be correct if the focus is only on alleviating congestion on, and around, the bridge. That option simply adds express lanes that bypass the bridge and three busy junctions. Despite the longer tunnels, using TBMs, it would turn out to be lower in both cost and all adverse impacts.

However, the NH proposal partially unloads the Dartford crossing and then does more. It's a short-cut for N-SE traffic, and provides bonus local connections. Now-deleted local connections (eg. Tilbury) north of the river would have further exploited this tunnel, at relatively low cost.

You're into the problems of induced demand though with the current proposal, which is mainly why several of the local connections were deleted. We don't need more car commuting across the river; if these local trips need to be made then there needs to be rapid transit options that don't involve unloading another 100,000 AADT onto existing congested networks.

[jackal]

... I would say that a now forgotten option, Option A14 (as a part of the options under, well, Option A) could be a better route than the one National Highways is currently opting for, ...

I think your analysis may be correct if the focus is only on alleviating congestion on, and around, the bridge. That option simply adds express lanes that bypass the bridge and three busy junctions. Despite the longer tunnels, using TBMs, it would turn out to be lower in both cost and all adverse impacts.

However, the NH proposal partially unloads the Dartford crossing and then does more. It's a short-cut for N-SE traffic, and provides bonus local connections. Now-deleted local connections (eg. Tilbury) north of the river would have further exploited this tunnel, at relatively low cost.

The bored tunnel for this option appears to be some 7.5 miles, three times longer than the proposal. On the other hand it would require less new road and less complex junctions than the proposed scheme. Conveniently the current scheme contracts are broken up into £1.3bn North of the Thames, £600m Kent, and £2.1bn Tunnelling. Assuming a similar D3 standard this allows a rough contract cost estimate of £6.5bn - £6bn for the proposed tunnels and portals, and £500m for the junctions and widening (which would be needed up to J3 and J29 at least). This is 23% more than the £5.3bn contract cost for the LTC as developed. (The LTC is sometimes described as £8.2bn, which is the upper range limit and includes elements not present in the main works contracts; the alternative scheme would be £10.1bn on the same basis.)

If it were 2012 I would say either this or the chosen option would be reasonable. It has obvious benefits (e.g., greater reduction in A282 traffic and lower environmental impact) and disbenefits (e.g., loses the dramatic reduction in journey times between Kent and Essex, does not relieve the A2, A13 or J30, probable higher cost).

But it isn't 2012, and we've been through a lengthy process of scheme development and consultation to make this kind of determination, the result of which is the proposed scheme. There have been countless opportunities to propose alternatives over the last decade and the present scheme was selected over all of them, including the one proposed here. Attempts to reopen that process now come across as spoiler tactics aiming to stop any improvement for the foreseeable future rather than a genuine concern with transport issues in the area. (Likewise mass transit alternatives, which have been explored extensively and are simply not a credible way of relieving an orbital motorway with a high proportion of goods vehicles in a suburban to rural setting.)

[Peter Freeman]

You're into the problems of induced demand though with the current proposal, which is mainly why several of the local connections were deleted. We don't need more car

Lots of HGVs on this route

commuting across the river; if these local trips need to be made

They do need to be made. Many of us enjoy driving, but few trips are recreational

then there needs to be rapid transit options that don't involve unloading another 100,000 AADT onto existing congested networks.

"Let's socially-engineer travellers onto buses and trams by making driving hell".

(Yes, we need public transport, but also private end-to-end transport and commercial/goods transport. Building this road, even with collateral local benefits, doesn't preclude public transport provision).

[Peter Freeman]

EDIT: A version of the U-turn without the reconfigured braiding. This is a less complicated change to the NH proposal, but is less good as the U-turn traffic would have to be signalised.

In principle, I don't mind a GSJ including the odd signalised component. I think it's occasionally a pragmatic decision justified on cost or safety grounds. I feel I'm in a minority with this view: purists on Sabre will disagree with me. However, by analogy, the UK, has always accepted that motorways can include roundabouts, even at a system interchange, which amounts to the same thing.

Your example near to your LTC U-turn would lower the cost, and not be very detrimental to performance. At that complex and already-expensive spaghetti junction though, saving 'small-change' by eliminating one bridge would be churlish.

It will be interesting to see how this interchange finally turns out (if it ever does!). On design-and-construct contracts, the contractor quite often introduces clever improvements over the reference design. They could borrow some of ours.

[Peter Freeman]

... Despite the longer tunnels, using TBMs, it would turn out to be lower in both cost and all adverse impacts. ...

The bored tunnel for this option appears to be some 7.5 miles, three times longer than the proposal. ...
... This is 23% more than the £5.3bn contract cost for the LTC as developed.

My estimate that the option A14 total cost would be lower than the current plan was my own amateur estimate, based on the simplicity of the task: one twin tunnel, two TBMs, two over-bridges for the forks, and a bit of M25 widening here and there. TBMs are expensive, but not all that expensive. Immersed tube segments are also expensive, and tricky to handle. The technology and usage of TBMs seems to be quickly advancing. However, I accede to your more rigorous estimating.

I was also influenced by hearing a rumour, mid-this-year, that the Sydney Western Harbour Tunnel, planned so far to be immersed tube, was considering a switch to TBM. Today, that rumour was confirmed -
https://www.smh.com.au/national/nsw/maj ... 5bv0g.html

[RichardA35]

A lot of off topic messages have been moved to another topic.
Please only post messages relevant to the LTC in this topic.
Thanks
SMT