There is no Tilbury link in the current version: https://highwaysengland.citizenspace.co ... ements.pdfPeter Freeman wrote: ↑Sun Mar 20, 2022 12:19That 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north of the river, serving Tilbury and a service area, is shown on one of the fly-throughs (perhaps I'm watching an out-of-date video?).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 . I presume left turn bypasses . I suspect signalisation . I wonder whether any consideration was given to replacing it ...?
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 ).
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!
1. Yes, two left turn freeflow filters and full signalisation (it's already half signalised). It's a solid upgrade and it was never realistic to expect more given the state of the A127. If the LTC had to solve all nearby road problems it would never get built.
2. I feel the design is noticeable actually for how little carriageway width drops through major junctions. A large majority of the time a hard shoulder is provided for, I suppose, maintenance and future proofing. At the A2 junction there is even a hard shoulder and an extra lane of hatching provided eastbound.
3. If you look at earlier designs for the M25 junction, the LTC northbound crosses the railway and back again, which would have allowed it to merge into the M25 a bit earlier and removed the need for braiding. But the cost and hassle of two additional railway bridges is really not worth it, hence the current design, which has the LTC northbound running parallel to the railway rather than crossing it, and merging in a bit later. Even so, I agree, the braiding is not absolutely required as the spacing isn't very tight, but they are to be applauded for providing it as it will greatly smooth the flow of traffic at the very high volumes and HGV % on this section of the M25, and it only requires one bridge (admittedly skewed).
4. I'm not really seeing any very long single lane connectors? The longest I can see is LTC to A127, which is quite long but not really enough to justify two lanes with a conflict point where the second lane drops.
5. It's very ambitious IMO. The main sticking point is "only" having three lanes through the tunnel, but that's understandable for the technical reasons rehearsed in my previous post. And in any event the more pressing pinch points will be off the route itself, for instance on the M25 north of J29, on the A13 east, and the A229 at Blue Bell Hill. If the LTC were somehow built on a significantly larger scale with a four lane tunnel it would simply have capacity that could never be utilised due to all the other constraints - and those constraints would be less likely to be eased as the LTC would have sucked up all the funding. For instance, you can see from the design of the LTC/A13 junction that traffic is funnelled onto the A13 more than the LTC (i.e., two turns to/from the A13, only one to/from the LTC), and the A13 is only three lanes after the current upgrade, and even drops to two a couple of junctions along. A D4 tunnel would be fabulously expensive and something of a white elephant given the surrounding network.
My complaints are smaller, mostly to do with the weird Tilbury access. They should either not have any direct access, with that to come with the future scheme, or provide it in both directions. I can't see any scenario where access in one direction makes sense - it's not enough if the future scheme doesn't happen, and redundant if it does.