M56 new Junction 11a

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wrinkly
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Re: M56 new Junction 11a

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jackal
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Re: M56 new Junction 11a

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wrinkly wrote:Exhibition boards now up.

http://assets.highways.gov.uk/roads/roa ... t+2016.pdf
I never will understand the widespread UK practice of grade-separating a road everywhere except its busiest junction...
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wrinkly
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Re: M56 new Junction 11a

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It appears that the east option involves replacing the existing bridge because it doesn't have room for slip road tapers beneath.
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Re: M56 new Junction 11a

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jackal wrote:
wrinkly wrote:Exhibition boards now up.

http://assets.highways.gov.uk/roads/roa ... t+2016.pdf
I never will understand the widespread UK practice of grade-separating a road everywhere except its busiest junction...
Looking at the plans has given me a twitchy eye and I'm going to have to lie down in a dark room for a bit.

To put it very mildly... I don't care for either design!
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Bryn666
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Re: M56 new Junction 11a

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Both are underwhelming but at least the east option reduces weaving between 11a and 12. There are a lot of conflicting movements though and I can see it being very congested if not signalled correctly.

The west option is less complex and more intuitive to use but will have weaving problems and also low capacity under the railway between two roundabouts (the southernmost has a redundant section that no one will ever use too).

In an ideal world there'd just be a fork junction...
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ais523
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Re: M56 new Junction 11a

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The east option confuses me because of the full hamburger. I wouldn't expect many drivers to use that hamburger westbound, whereas the M56 westbound to A533 westbound movement (which must surely be one of the most popular) is marginalised. A half-hamburger would be more believable (although still disappointing).

The west option seems rather more reasonable, although I'm a little worried about safety. I'd expect signalisation at the end of the westbound offslip from the M56 (in the style of the M32/M4 junction) to avoid a conflict between traffic that's leaving the M56 westbound and trying to get to lane 1 for the roundabout, and traffic trying to join the M56 westbound in lane 2. (This may be fixable with careful lane assignments, or even reducing the southbound entrance to the roundabout, as well as the eastern arc of the roundabout itself, to one lane; two is the obvious assumption but isn't the only way to mark the roundabout and one would probably be enough for the movements that go that way.)
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Re: M56 new Junction 11a

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Is there any particular reason why they can't just GSJ the present roundabout at the end of the Southern Expressway and continue the road on as east-facing motorway slip roads?
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Re: M56 new Junction 11a

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jackal wrote:I never will understand the widespread UK practice of grade-separating a road everywhere except its busiest junction...
If the Runcorn Expressways had been designed in the 80s rather than the 60s they would have had flat roundabouts, some of which would no doubt by now have been replaced by signalised junctions :(
vlad wrote:Is there any particular reason why they can't just GSJ the present roundabout at the end of the Southern Expressway and continue the road on as east-facing motorway slip roads?
I don't think there's any room for the necessary westbound offslip and bridge because there are now buildings in the way. It could have been done when the M56 was opened, of course.

As I said earlier in the thread, the two options on the table are different flavours of dog's dinner.
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Re: M56 new Junction 11a

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PeterA5145 wrote:
vlad wrote:Is there any particular reason why they can't just GSJ the present roundabout at the end of the Southern Expressway and continue the road on as east-facing motorway slip roads?
I don't think there's any room for the necessary westbound offslip and bridge because there are now buildings in the way. It could have been done when the M56 was opened, of course.
I you really wanted to you could do it now by realigning the M56 mainline to create space on the other side.
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Re: M56 new Junction 11a

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I don't see the need for full access at this junction; most users from the west (Chester/Wirral/Wales) will still use J12; it's only those from the east who will use this in preference to J11.

There's less than a mile between this new junction and both of the existing ones either side. That seems a short distance for three junctions.

The east option is better for the eastbound on-slip directly from the Southern Expressway, but the slip roads on the south side of the motorway look very short and onto a small roundabout. With the existing A56/A533 roundabout to the east towards the industrial estate, it could back up and block the exit from the roundabout and cause queuing on the mainline.

The west option at least takes the junction onto a spur road. It also gives a better opportunity to sort out the whole A56 overpass and Murdishaw roundabout. Do I see a 'developer' road in this layout, opening up land for some kind of business or retail park south of Sutton Weaver?
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Re: M56 new Junction 11a

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Shed development in the way and a steadfast refusal to purchase them for roads I believe... :laugh:

Bet the west option goes ahead on build ability grounds.
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Re: M56 new Junction 11a

Post by Truvelo »

Both options are rather low rent but I guess that's the reality of the 21st century. Of the two the eastern proposal is marginally better. A pity the hamburger, at least eastbound, wasn't proper grade separation as it would allow the expressway to flow seamlessly onto the M56. Westbound would be tricky due to the close proximity of the sharp curve.
How would you like your grade separations, Sir?
Big and complex.
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Re: M56 new Junction 11a

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Hugo Nebula wrote: The east option is better for the eastbound on-slip directly from the Southern Expressway, but the slip roads on the south side of the motorway look very short and onto a small roundabout. With the existing A56/A533 roundabout to the east towards the industrial estate, it could back up and block the exit from the roundabout and cause queuing on the mainline.
There's a similarly short space between the Murdishaw rbt and A56 T-junction, which could result in queuing across the rbt with knock on queues for the eastbound M56.

The western option doesn't have any potential for queues of this sort and effectively grade separates the A56<->A56 movement from the Southern Expressway<->M56 movement. Yes, the spacing to J12 is tighter, but what you lose there you gain by increasing the spacing to J11, which is arguably more important as the M56 will be busier between J11 and J11a than it will be between J11a and J12.

While I think the western option is the least bad of the two, clearly this should be a limited access freeflow junction. It could be built as a kind of hybrid of the East and West options. The onslip could be built on a similar line to the East option eastbound onslip (but grade separated from the roundabout). The offslip could be built on a similar line to the West option westbound offslip, with a loop to get it pointing in the right direction, going under the A56 and merging into the Southern expressway from the left (or as a lane gain). Compared to a simple fork, this would have no need for demolition, and extends the weaving space between J11 and J11a westbound.
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Re: M56 new Junction 11a

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That's far too sensible...
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Re: M56 new Junction 11a

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Here's my hybrid of the East and West options with freeflow for M56E<->Southern Expressway. In the end I was able to make it full access. The only additional structural content compared to the West option is the bridge over the roundabout.
Image
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Re: M56 new Junction 11a

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If you move the eastbound exit slip to be where it is in the official west option then the existing A56/A533 over M56 bridge will have no slip road tapers under it, so any need to replace it is removed.
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Re: M56 new Junction 11a

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wrinkly wrote:If you move the eastbound exit slip to be where it is in the official west option then the existing A56/A533 over M56 bridge will have no slip road tapers under it, so any need to replace it is removed.
If I put it there it would conflict with the diverge for the southern expressway.

I thought the reason the existing bridge was being replaced in the East option was to make space for the slips on the westbound carriageway, which are not there on my plan. I doubt the bridge would need replacement just to accommodate the eastbound diverge to the roundabout. It would be a simple single lane diverge and the nose would certainly be to the east of the bridge, meaning at most one lane width extra (probably less) under the bridge would be required. That can be reclaimed from the HS under the bridge as necessary.
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Re: M56 new Junction 11a

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jackal wrote:Here's my hybrid of the East and West options with freeflow for M56E<->Southern Expressway. In the end I was able to make it full access. The only additional structural content compared to the West option is the bridge over the roundabout.
Can we register you as a consultant for Highways England? This is much better!
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jackal
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Re: M56 new Junction 11a

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Chris5156 wrote:
jackal wrote:Here's my hybrid of the East and West options with freeflow for M56E<->Southern Expressway. In the end I was able to make it full access. The only additional structural content compared to the West option is the bridge over the roundabout.
Can we register you as a consultant for Highways England? This is much better!
If only my MS Paint skills could do it justice :)
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Re: M56 new Junction 11a

Post by Truvelo »

If I have time I could give it a go.

The eastbound exit slip not freeflowing onto the expressway isn't a problem as it's a minor traffic flow compared to the westbound M56. It's clearly the best design I've seen and I couldn't do any better unless we're talking huge budgets.
How would you like your grade separations, Sir?
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