M56 new Junction 11a

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jackal
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Re: M56 new Junction 11a

Post by jackal »

Truvelo wrote:If I have time I could give it a go.
That would be great :thumbsup:
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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.
Image
The levels may be a bit of a git around the railway but this design is far superior.

We seem to be allergic to free flow designs, the abominations proposed on the M42 around the NEC are another example.
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Stevie D
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Re: M56 new Junction 11a

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Working on the realistic basis of affordability, how does this look as a viable compromise? It only has east-facing links to the motorway because, as others have noted, access between M56(W) and Runcorn would still usually be best via J12, so there is little need for west-facing slips, and omitting them allows a much simpler junction.

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Re: M56 new Junction 11a

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It's a fairly good effort - the roundabout for westbound exit may be an issue.

The big problem is you've demolished all the new shed development. Naughty naughty!
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Stevie D
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Re: M56 new Junction 11a

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Bryn666 wrote:It's a fairly good effort - the roundabout for westbound exit may be an issue.

The big problem is you've demolished all the new shed development. Naughty naughty!
What don't you like about the roundabout for the westbound exit?
Aren't those shed developments likely to be demolished under the eastern proposal anyway? That's why I assumed they were sacrificial!

I've done a second draft, getting rid of both new roundabouts – I think the one to the north could potentially be replaced with a priority T-junction (I don't know how busy Murdishaw Avenue is as to whether that's going to be sensible, but it's easy enough to reinstate the roundabout on the design if necessary, or signalise the junction) - and the one to the south might work better as a signalised crossroads, given the unbalanced nature of the flows (it might be difficult for traffic coming from Preston Brook to get onto the roundabout given that there will never be any traffic coming off there).

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Re: M56 new Junction 11a

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The biggest problem I see with that design is the end of the westbound offslip. Traffic will want to be continuing west there at fairly high speed, and yet those vehicles will need to try to cross the road as part of their right turn. I guess you could give them priority and force cars going around locally to find gaps to cross, but that would likely be exceptionally dangerous and run the potential risk of forming long queues at busy times. (You could also reverse the carriageways of the road in question to avoid the problem, but people tend to be suspicious of plans which have roads which are driven on on the right.)

EDIT: And here's my attempt. Mapping data © OpenStreetMap contributors.
My plans for a new M56 J11A
My plans for a new M56 J11A
The curve on the "jughandle" that allows the westbound offslip to cross the motorway at 90 degrees isn't meant to be as tight as I've drawn it. (Even so, it's intended to have an advisory 45mph limit just for the curve, to allow it to be made smaller.) M56 to A533 westbound to westbound, and A533 to M56 eastbound to eastbound, are free-flowing. If you want to leave the M56 westbound but not freeflow onto the expressway, you can take the slip road down to a new signalised junction with the A56 (I also added the farm access to the junction, for safety reasons because the extra bridge reduces visibility; there are I think ways to phase the junction so that the farm access doesn't slow down other traffic or need a phase of its own). Access to the M56 eastbound is also possible from anywhere (but only the A533 gets a freeflow). If you want to access the M56 in the other direction, use junction 12.
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Stevie D
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Re: M56 new Junction 11a

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ais523 wrote:The biggest problem I see with that design is the end of the westbound offslip. Traffic will want to be continuing west there at fairly high speed, and yet those vehicles will need to try to cross the road as part of their right turn. I guess you could give them priority and force cars going around locally to find gaps to cross, but that would likely be exceptionally dangerous and run the potential risk of forming long queues at busy times.
Is it likely to be that big a deal?

I would have thought that a 50 or even 40 limit applying on the westbound side (where the existing road bridges across the M56) would be sufficient, and would allow the small amount of traffic coming off the M56 and wanting the A56 for Frodsham the chance to get across to lane 1 before the split approaching the traffic lights. Given that the majority of traffic for Frodsham would be directed via J12, that's likely to be a pretty niche movement. Apart from that, you have the lane from the slip road and one lane from the roundabout continuing straight across onto A533, and traffic from the roundabout wanting Murdishaw should have plenty of time to get in the right-hand lane.

Image

My bigger concern would be eastbound, where traffic coming round the spiral at probably only about 30mph doesn't have that long a weaving section before its lane gain becomes a lane drop and peels off to the M56. It may be that (depending on volume of traffic) the lane gain could be replaced by a give way, or a signal-controlled merge, eliminating the need for weaving.
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Re: M56 new Junction 11a

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Stevie D wrote:Is it likely to be that big a deal?

I would have thought that a 50 or even 40 limit applying on the westbound side (where the existing road bridges across the M56) would be sufficient
Oh, I'd missed that the road that's being merged into was one-way. I thought you were trying to merge traffic into the far side of a bidirectional road. The design makes more sense now.
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Re: M56 new Junction 11a

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ais523 wrote:Oh, I'd missed that the road that's being merged into was one-way. I thought you were trying to merge traffic into the far side of a bidirectional road. The design makes more sense now.
No, that would be crazy and would need a capacity-sapping signal-controlled crossing and merge (or, as you said, wrong-side running, which would be problematic and courageous, to say the least). Making it one-way makes the merge smoother and gives much higher capacity, but the downside is the need for the Carousel-like spiral onto the eastbound flyover.
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Re: M56 new Junction 11a

Post by PeterA5145 »

Obviously it's much easier to design a junction with only east-facing slips, but I assume traffic surveys and modelling have identified sufficient demand to make west-facing slips worthwhile to serve traffic not only from the industrial estate but also the Northwich area.
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Re: M56 new Junction 11a

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Perhaps the west option as a trumpet would be best but that would take up precious building land for more tin sheds :roll:
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Re: M56 new Junction 11a

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Here is Jackal's design drawn to scale. I've had to make a couple of modifications to get everything to fit with acceptable radii. Firstly the southern side of the roundabout has been enlarged to accommodate the fifth arm. The A56/A533 bridge over the M56 has moved eastwards to allow the approach to the roundabout to take its new 4'o'clock position. This bridge would be replaced anyway in one of the official designs.
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Re: M56 new Junction 11a

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I really, really like that design.

One thought - going over the motorway and then under the railway might create a bit if a roller coaster? We'd need to see the levels I suppose to make an informed decision.
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Re: M56 new Junction 11a

Post by Truvelo »

That did cross my mind but looking at contours on OS maps and streetview images proved inconclusive so I simply used Jackal's suggestions. The M56 is in a cutting so that's an obvious choice but the railway is on an embankment so going over that might end up with a steep climb and than a fall to reach the roundabout.
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Re: M56 new Junction 11a

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Really good job with the design :D My only query would be whether it's really necessary to replace the current bridge over the M56. Would it not be possible to just bend the road coming north over the bridge to the right earlier (using the space of the bridge's wide central reservation), then left as it approaches the roundabout, so they meet at the correct angle? The bridge itself is barely longer than the width of the M56 so there's quite a lot of space to get the A533 pointing in the right direction before the roundabout.
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Re: M56 new Junction 11a

Post by Truvelo »

What I've found when drawing maps is it's easy to make sharp curves which look alright on a map but are extremely sharp in reality. Leaving the bridge where it was would result in a sharp right curve followed by a left plus the junction with the A56 would be between these, see Bryn's comment in the Laurencekirk GSJ thread about gaps on bends. The bridge itself would have to be replaced to allow space for the taper below so it might as well be shifted to a better location.

This map shows how bad the kink would be if the original bridge was left in place.
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Re: M56 new Junction 11a

Post by Bryn666 »

In any case the amount of barrier and stripey paint on the existing bridge suggests it's worn somewhat and would be better replaced.
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Re: M56 new Junction 11a

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Consultation opens 16 January:

http://roads.highways.gov.uk/projects/m ... ction-11a/

The options are described like this:

Option A – Upgrading Murdishaw roundabout into a through-about
Option B – Converting Murdishaw roundabout into a signalised crossroad

From this it sounds like the previous 'West option' has been dropped, and the consultation is to decide what kind of signalised junction the 'East option' will have (hamburger or crossroad).
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Re: M56 new Junction 11a

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A three year wait after the end of the consultation before work starts... we don't like to crack on do we with planning and design... :roll:
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Re: M56 new Junction 11a

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