New Lower Thames Crossing

[jackal]

The new 'local refinement' consultation is open. While the road design is largely as before there are a few differences:

1. As anticipated, there's a new slip connecting Orsett Cock to the A1089. This has quite wide ranging implications, as not only local traffic but northbound and southbound LTC traffic can now access the A1089 via a U-turn at Orsett Cock. This new connectivity comes at a cost, as the direct link from the westbound A13 to the A1089 has had to make way (the movement can still be performed via Orsett Cock). Here's the before and after:

So basically one freeflow movement is sacrificed for the sake of several at-grade movements. On balance I think it's a decent trade, as A13 westbound to A1089 does not seem to be a huge movement (<250 PCU in a peak hour), and there were some notable missing movements in the previous design that, as shown above, would have forced strategic traffic heading for the A1089 onto local roads.

2. The Tilbury GSJ has returned, this time for operational access, though "with possible future development in mind, helping to avoid potentially disruptive re-work at a later date. ... Any new road connecting to the LTC at this point would have to follow the relevant planning process at the appropriate time". I think it's okay really. It does make sense for NH and emergency services to be able to turn around near the tunnel, and it would save some further work on the LTC in the event of the Tilbury link road. Even so, I think some work would be required, as it's quite a skimpy folded diamond with a single carriageway bridge and link roads.

3. It doesn't seem to be mentioned in the guide, but I noticed that the M25 between the LTC and A127 now has full hard shoulders. They were discontinuous in the previous design, to the point of being ALR-like southbound, which is of course verboten.

Consultation: https://highwaysengland.citizenspace.co ... tion-2022/
Guide: https://highwaysengland.citizenspace.co ... tation.pdf
Interactive map: https://ltcconsultation2022.nationalhighways.co.uk/map/
General arrangements: https://highwaysengland.citizenspace.co ... ements.pdf

[RichardA35]

The new 'local refinement' consultation is open. While the road design is largely as before there are a few differences:

1. As anticipated, there's a new slip connecting Orsett Cock to the A1089. This has quite wide ranging implications, as not only local traffic but northbound and southbound LTC traffic can now access the A1089 via a U-turn at Orsett Cock. This new connectivity comes at a cost, as the direct link from the westbound A13 to the A1089 has had to make way (the movement can still be performed via Orsett Cock). Here's the before and after:

So basically one freeflow movement is sacrificed for the sake of several at-grade movements. On balance I think it's an okay trade, as A13 westbound to A1089 does not seem to be a huge movement (<250 PCU in a peak hour), and there were some notable missing movements in the previous design that, as shown above, would have forced strategic traffic heading for the A1089 onto local roads.

I may have mentioned this before but (from a guy at the exhibition) there was so much uncertainty about the local developments in the area, coupled with the unknown LTC traffic flows, that the design of Orsett Cock roundabout was only to cater for design traffic at opening year.
With the extra movements highlighted, hopefully there will be some subtractions so that the roundabout will still work without another major rebuild.

[jackal]

The new 'local refinement' consultation is open. While the road design is largely as before there are a few differences:

1. As anticipated, there's a new slip connecting Orsett Cock to the A1089. This has quite wide ranging implications, as not only local traffic but northbound and southbound LTC traffic can now access the A1089 via a U-turn at Orsett Cock. This new connectivity comes at a cost, as the direct link from the westbound A13 to the A1089 has had to make way (the movement can still be performed via Orsett Cock). Here's the before and after:

So basically one freeflow movement is sacrificed for the sake of several at-grade movements. On balance I think it's an okay trade, as A13 westbound to A1089 does not seem to be a huge movement (<250 PCU in a peak hour), and there were some notable missing movements in the previous design that, as shown above, would have forced strategic traffic heading for the A1089 onto local roads.

I may have mentioned this before but (from a guy at the exhibition) there was so much uncertainty about the local developments in the area, coupled with the unknown LTC traffic flows, that the design of Orsett Cock roundabout was only to cater for design traffic at opening year.
With the extra movements highlighted, hopefully there will be some subtractions so that the roundabout will still work without another major rebuild.

If you look at the maps from p. 81 below there is >40% increase on much of the Orsett Cock roundabout as a result of the scheme. The roundabout itself is not changed by the LTC scheme. They did at least widen the whole roundabout to three lanes under the current scheme though I'm not sure that that will be enough.

https://highwaysengland.citizenspace.co ... tation.pdf

[RichardA35]

If you look at the maps from p. 81 below there is >40% increase on much of the Orsett Cock roundabout as a result of the scheme. The roundabout itself is not changed by the LTC scheme. They did at least widen the whole roundabout to three lanes under the current scheme though I'm not sure that that will be enough.

Indeed, that was my point, that the roundabout will be at capacity with forecast local traffic flows now (it was designed for flows at opening year of the A13 widening and it is the southern section that performs worst) and that the proposed LTC traffic, which all seems to be additions, will only add to its woes.

[Truvelo]

The A13 junction seems to be getting ever more complex at each consultation. It's beginning to look like some of the overblown fantasy maps many of us here would draw.

[jackal]

If you look at the maps from p. 81 below there is >40% increase on much of the Orsett Cock roundabout as a result of the scheme. The roundabout itself is not changed by the LTC scheme. They did at least widen the whole roundabout to three lanes under the current scheme though I'm not sure that that will be enough.

Indeed, that was my point, that the roundabout will be at capacity with forecast local traffic flows now (it was designed for flows at opening year of the A13 widening and it is the southern section that performs worst) and that the proposed LTC traffic, which all seems to be additions, will only add to its woes.

Interestingly, though, the west side of the roundabout is significantly less busy with the scheme than without. I'd suggest the circulatory could be narrowed to 2 lanes there and a cheeky U-turn facility added, so LTC>A1089 traffic can bypass the roundabout, like this: https://www.google.co.uk/maps/@55.85018 ... 384!8i8192

[jackal]

A Decade of A13 Interchange Designs:

2012:

2016:

2017:

[jackal]

2018:

2020:

2022:

[Keiji]

1. As anticipated, there's a new slip connecting Orsett Cock to the A1089. This has quite wide ranging implications, as not only local traffic but northbound and southbound LTC traffic can now access the A1089 via a U-turn at Orsett Cock. This new connectivity comes at a cost, as the direct link from the westbound A13 to the A1089 has had to make way (the movement can still be performed via Orsett Cock). Here's the before and after:

[...]

So basically one freeflow movement is sacrificed for the sake of several at-grade movements. On balance I think it's a decent trade, as A13 westbound to A1089 does not seem to be a huge movement (<250 PCU in a peak hour), and there were some notable missing movements in the previous design that, as shown above, would have forced strategic traffic heading for the A1089 onto local roads.

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

There appears to be plenty of space, the vertical alignment should be fine given they already both bridge over another road, and there are no weaving issues either before the additional diverge, or after the additional merge.

That said, traffic from the roundabout still can't access the N/B or S/B LTC, while the reverse is easily possible; I'm not sure what you'd do about that one. The more I look at it, the weirder it seems...

Glad to see the Tilbury junction back, though.

[jackal]

1. As anticipated, there's a new slip connecting Orsett Cock to the A1089. This has quite wide ranging implications, as not only local traffic but northbound and southbound LTC traffic can now access the A1089 via a U-turn at Orsett Cock. This new connectivity comes at a cost, as the direct link from the westbound A13 to the A1089 has had to make way (the movement can still be performed via Orsett Cock). Here's the before and after:

[...]

So basically one freeflow movement is sacrificed for the sake of several at-grade movements. On balance I think it's a decent trade, as A13 westbound to A1089 does not seem to be a huge movement (<250 PCU in a peak hour), and there were some notable missing movements in the previous design that, as shown above, would have forced strategic traffic heading for the A1089 onto local roads.

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

slip.png

There appears to be plenty of space, the vertical alignment should be fine given they already both bridge over another road, and there are no weaving issues either before the additional diverge, or after the additional merge.

That said, traffic from the roundabout still can't access the N/B or S/B LTC, while the reverse is easily possible; I'm not sure what you'd do about that one. The more I look at it, the weirder it seems...

Glad to see the Tilbury junction back, though.

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.

Re: Tilbury, you have to wonder why they have still included the complex A1089 to LTC south movement at the A13 junction when they clearly plan to replace it with a more direct link.

[frediculous_biggs]

Re: Tilbury, you have to wonder why they have still included the complex A1089 to LTC south movement at the A13 junction when they clearly plan to replace it with a more direct link.

How many examples are there across the country of bits of roads being designed such that "this will be built later" and it turns out never to be. I'd much rather they got it right and assumed nothing about future developments.

[jackal]

Re: Tilbury, you have to wonder why they have still included the complex A1089 to LTC south movement at the A13 junction when they clearly plan to replace it with a more direct link.

How many examples are there across the country of bits of roads being designed such that "this will be built later" and it turns out never to be. I'd much rather they got it right and assumed nothing about future developments.

Well, I'd agree if the design "got it right", but going from Tilbury to East Tilbury (where the LTC tunnel will come up) via the A13 is very circuitous - two sides of a triangle.

The more I look at it the more I think they should have gone for LTC route 2, which would have merged with the A1089 north of Tilbury, providing an 'automatic' high quality route to Tilbury via the junction there, and a much easier configuration for the A13 junction, which would just be a four way freeflow junction rather than the five way+Orsett Cock mess they are forced into now.

Admittedly, I wasn't especially keen on route 2 at the time as it's slightly longer on a map and I hadn't considered that it would simplify so many movements - probably others thought the same as it wasn't chosen. (I actually liked route 4 the most, though that's a different beast altogether.)



Anyway, too late for that now - the design does a decent job with the hand they've been dealt, and will be a massive improvement in connectivity.

[Truvelo]

Admittedly, I wasn't especially keen on route 2 at the time as it's slightly longer on a map and I hadn't considered that it would simplify so many movements - probably others thought the same as it wasn't chosen. (I actually liked route 4 the most, though that's a different beast altogether.)

Were any detailed plans drawn up for the alternative routes? Would Route 4 have simply transferred the problem junction to M25 J29 instead which is hemmed in by businesses on the eastern side of the junction making a freeflow north to east link difficult without demolition. The A127 would also need parallel carriageways either as C/D or similar to the A1-A14 setup south of Brampton Hut. At least with route 3 we get to have a nice five way spaghetti bowl at Orsett

[Peter Freeman]

Interestingly, though, the west side of the roundabout is significantly less busy with the scheme than without. I'd suggest the circulatory could be narrowed to 2 lanes there and a cheeky U-turn facility added, so LTC>A1089 traffic can bypass the roundabout, like this: https://www.google.co.uk/maps/@55.85018 ... 384!8i8192

That's a good idea. Even better, leave the circulatory alone, but add one parallel single-lane bridge for that u-turn.

[Peter Freeman]

(I actually liked route 4 the most, though that's a different beast altogether.)

Me too. It included a 4-level stack at A13.

[For] Route 4, [the] A127 would also need parallel carriageways, either as C/D or similar to the A1-A14 setup south of Brampton Hut.

Maybe; but with 3 or 4 km to weave, perhaps a D4 or D5 or D6 expansion would suffice. Most eastbound traffic from M25 southbound would aim for LTC (enter on left and diverge left), and most eastbound traffic from A127 would aim for A127 (continue straight-on). Since entries and exits are on the left in both directions, as they should be, it's not one of those situations where everyone wants to swap sides: only those driving down the middle. This assumes that the advance signage, the gantry signage and the lane discipline are all good.

At least with route 3 we get to have a nice five way spaghetti bowl at Orsett

Stacks trump spaghetti bowls.

[jackal]

Were any detailed plans drawn up for the alternative routes? Would Route 4 have simply transferred the problem junction to M25 J29 instead which is hemmed in by businesses on the eastern side of the junction making a freeflow north to east link difficult without demolition. The A127 would also need parallel carriageways either as C/D or similar to the A1-A14 setup south of Brampton Hut. At least with route 3 we get to have a nice five way spaghetti bowl at Orsett

Yes, there are detailed plans, which are probably still online from the 2016 consultation (in the Volume 3 Appendices IIRC). Here are the major junctions for Route 4, comprising the A13 stack Peter mentions, a big fork at the A128 and an upgraded M25 J29:

The A127 mainline is indicated as D4. Bear in mind this is when the LTC itself was planned as D2. With a D3 LTC a D5 A127 might have been sufficient, considering there are no intermediate junctions and there's an LAR along the whole section, though C/D lanes would be preferable.

[jackal]

Interestingly, though, the west side of the roundabout is significantly less busy with the scheme than without. I'd suggest the circulatory could be narrowed to 2 lanes there and a cheeky U-turn facility added, so LTC>A1089 traffic can bypass the roundabout, like this: https://www.google.co.uk/maps/@55.85018 ... 384!8i8192

That's a good idea. Even better, leave the circulatory alone, but add one parallel single-lane bridge for that u-turn.

That is indeed better because it separates the U-turn traffic from pedestrians.

An issue with a U-turn is that it poses weaving issues on the eastbound slip; LTC traffic would have to weave across traffic from the A13 to get to the U-turn facility. Arguably the weaving is already there as traffic would have to get into lane for the roundabout even without the U-turn.

I actually have a more drastic idea: remove the proposed Orsett Cock diverge (shown by red Xs), so there is no braiding needed at that point. A13 traffic for Orsett Cock instead takes the A1089 diverge, which then has a further diverge (shown in red) leading to the outercarriageway. This way there is no weaving on the immediate approach to Orsett Cock roundabout because the A13 slip isn't coming in there. A further major advantage of this is that there's no weaving on the A13 mainline between the loop from the A1089 and the Orsett Cock diverge.

(Click to expand)

[Peter Freeman]

Route 4 A128 junction - Copy.PNG
Route 4 M25 junction - Copy.PNG

The A127 mainline is indicated as D4. Bear in mind this is when the LTC itself was planned as D2. With a D3 LTC a D5 A127 might have been sufficient, considering there are no intermediate junctions and there's an LAR along the whole section, though C/D lanes would be preferable.

My design for this 4km LTC/A127 duplex would not use C/D roads.

At the existing merge from the M25 J29 roundabout into A127 eastbound, I would grow the A127 eastbound to three lanes (on-ramp adds one lane). Also, where the LTC diverges from M25 southbound immediately before M25 J29, the off-connector would be 3 lanes wide. Yes, three! These two 3-lane carriageways, converging eastwards, would then merge, with no lane-loss, to form one half of a 4km-long D6 LTC/A127 duplex.

Preceding the merge, gantry signs would have assigned, on the LTC connector, two (left) lanes for LTC and one (right) lane for A127; and on the A127 through-route, would have assigned two (right) lanes for A127 and one (left) lane for LTC. The 6-lane duplex length following the merge now has stable traffic in its edge-lanes, and traffic wishing to swap sides is flowing down the two middle lanes. The latter have 4km in which to swap: no problem. Long-dash warning white lines between lanes 3 and 4 begin here.

At the eastern end of the duplex, the LTC would diverge left, with three lanes. Traffic continuing eastwards on the A127 would initially also have 3 lanes, but one would soon drop at the off-ramp diverge for the A128 elevated roundabout. East of this point, the A127 would remain D2.

There is obviously much scope for detailed changes to this description, and tuning. But you get the drift: lots of space.

In the opposite (northbound/westbound) direction of the LTC, similar, or 'complementary', lane arrangements would apply.

6 lanes on the duplex may sound extravagant, and probably is, purely in saturation flow arithmetic. But it facilitates the weave in the simplest and most driver-comprehensible way. C/D lanes, and also braiding, are not always obvious to drivers. Over-wide carriageways make life simpler, easier and safer for road users. I would be tempted to mildly speed-limit parts of this arrangement, to aid lane selection. For example, the off-connector that diverges left from the southbound M25. I am aware that this is rarely done in the UK, but it can provide opportunities for geometry concessions, and thereby extend weaving lengths.

All this of course is academic now - route 4 wasn't chosen.

[RichardA35]

..I actually have a more drastic idea: remove the proposed Orsett Cock diverge (shown by red Xs), so there is no braiding needed at that point. A13 traffic for Orsett Cock instead takes the A1089 diverge, which then has a further diverge (shown in red) leading to the outercarriageway. This way there is no weaving on the immediate approach to Orsett Cock roundabout because the A13 slip isn't coming in there. A further major advantage of this is that there's no weaving on the A13 mainline between the loop from the A1089 and the Orsett Cock diverge.

That's OK for the A13 eastbound but doesn't that remove the ability to get from Tilbury A1089 to the Orsett Cock and so onto the A128 to the hinterlands between Orsett and Brentwood?

[jackal]

..I actually have a more drastic idea: remove the proposed Orsett Cock diverge (shown by red Xs), so there is no braiding needed at that point. A13 traffic for Orsett Cock instead takes the A1089 diverge, which then has a further diverge (shown in red) leading to the outercarriageway. This way there is no weaving on the immediate approach to Orsett Cock roundabout because the A13 slip isn't coming in there. A further major advantage of this is that there's no weaving on the A13 mainline between the loop from the A1089 and the Orsett Cock diverge.

That's OK for the A13 eastbound but doesn't that remove the ability to get from Tilbury A1089 to the Orsett Cock and so onto the A128 to the hinterlands between Orsett and Brentwood?

Good point.

My design for this 4km LTC/A127 duplex would not use C/D roads.

At the existing merge from the M25 J29 roundabout into A127 eastbound, I would grow the A127 eastbound to three lanes (on-ramp adds one lane). Also, where the LTC diverges from M25 southbound immediately before M25 J29, the off-connector would be 3 lanes wide. Yes, three! These two 3-lane carriageways, converging eastwards, would then merge, with no lane-loss, to form one half of a 4km-long D6 LTC/A127 duplex.

Preceding the merge, gantry signs would have assigned, on the LTC connector, two (left) lanes for LTC and one (right) lane for A127; and on the A127 through-route, would have assigned two (right) lanes for A127 and one (left) lane for LTC. The 6-lane duplex length following the merge now has stable traffic in its edge-lanes, and traffic wishing to swap sides is flowing down the two middle lanes. The latter have 4km in which to swap: no problem. Long-dash warning white lines between lanes 3 and 4 begin here.

At the eastern end of the duplex, the LTC would diverge left, with three lanes. Traffic continuing eastwards on the A127 would initially also have 3 lanes, but one would soon drop at the off-ramp diverge for the A128 elevated roundabout. East of this point, the A127 would remain D2.

There is obviously much scope for detailed changes to this description, and tuning. But you get the drift: lots of space.

In the opposite (northbound/westbound) direction of the LTC, similar, or 'complementary', lane arrangements would apply.

6 lanes on the duplex may sound extravagant, and probably is, purely in saturation flow arithmetic. But it facilitates the weave in the simplest and most driver-comprehensible way. C/D lanes, and also braiding, are not always obvious to drivers. Over-wide carriageways make life simpler, easier and safer for road users. I would be tempted to mildly speed-limit parts of this arrangement, to aid lane selection. For example, the off-connector that diverges left from the southbound M25. I am aware that this is rarely done in the UK, but it can provide opportunities for geometry concessions, and thereby extend weaving lengths.

All this of course is academic now - route 4 wasn't chosen.

This is a decent idea but D6 is discouraged by DMRB - even D5 is in fact. 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.