M42 Junction 6 improvement

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Alderpoint
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Re: M42 Junction 6 improvement

Post by Alderpoint »

There have been a few changes (mostly minor) following the consultation earlier this year and further consulation has now opened.

Details here.
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Re: M42 Junction 6 improvement

Post by Bryn666 »

I'm too busy wincing at the "principle changes"... presumably they mean principal as the principle of the scheme is still the same.

Details... details... :roll:

Okay...

Junction 5A looks ridiculously small and seems to be an invitation for HGV rollover incidents. Also, there is a redundant bit of roundabout that will never see the light of day - the same happened on the A556, apparently it's "against DMRB" to just fill that bit in with grass since no-one will ever use it. Likewise - a dual carriageway overbridge is going to be half redundant unless the idea is to stick development here and completely undermine the purpose of relieving J6.

Catherine De Barnes Lane - does it really need access to the link road like that, why not just connect from the larger of the two J5A roundabouts? Seems to be expense for the sake of expense.

Traffic flows exiting the NEC towards the A45 eastbound now conflict with those entering it from J6 southbound which is likely to cause queues onto the M42. That's why the existing layout is a loop.

...

I give up.
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ais523
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Re: M42 Junction 6 improvement

Post by ais523 »

The layout of the Catherine de Barnes Lane connection is explicitly designed to avoid rat-running: the intention is that you can't get to the motorway from the side roads in the area without going all the way to the A45 and back again, thus removing the incentive to rat-run through the local villages. If you have that as a criterion of your plan, it's probably the cheapest way to do it while leaving the link road free-flow.

The intended route from the M42 southbound to the NEC will still be by means of the loop (which is being retained). So there isn't a conflict there.

I agree with you about the roundabouts, though. (There are some roundabouts on the A4510 that have sections that are usable only for U-turns from a minor direction. I went there in winter and they were covered in grit, because unlike the parts of the junction that vehicles actually use, there was nothing going along there to remove them. This will presumably end up similar.) The roundabouts were explained to me as "the radius is too small for drivers to treat it as a freeflow road, so we're putting a roundabout there so that drivers treat it like a roundabout and so it can have a smaller radius", but I'm not convinced that works unless there's actually a chance of conflicting traffic.
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Re: M42 Junction 6 improvement

Post by darkcape »

The East dumbbell of M1 J11a was changed during construction to infill the dead bit of roundabout, not sure why it can't be done here. The design team is the same, hence the similarity in junction layout...

The proposed service area is shown as off Solihull Road so unless a major redesign of 5a is expected how will it connect to the motorway? Or (again similar to J11a) the attempts at discouraging rat-running will be undermined by a developer-funded direct connection to the motorway network.
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Re: M42 Junction 6 improvement

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ais523 wrote: Tue Sep 04, 2018 18:20 The layout of the Catherine de Barnes Lane connection is explicitly designed to avoid rat-running: the intention is that you can't get to the motorway from the side roads in the area without going all the way to the A45 and back again, thus removing the incentive to rat-run through the local villages. If you have that as a criterion of your plan, it's probably the cheapest way to do it while leaving the link road free-flow.

The intended route from the M42 southbound to the NEC will still be by means of the loop (which is being retained). So there isn't a conflict there.

I agree with you about the roundabouts, though. (There are some roundabouts on the A4510 that have sections that are usable only for U-turns from a minor direction. I went there in winter and they were covered in grit, because unlike the parts of the junction that vehicles actually use, there was nothing going along there to remove them. This will presumably end up similar.) The roundabouts were explained to me as "the radius is too small for drivers to treat it as a freeflow road, so we're putting a roundabout there so that drivers treat it like a roundabout and so it can have a smaller radius", but I'm not convinced that works unless there's actually a chance of conflicting traffic.
The revised plans don't show a loop. They show a slip leaving the M42 sb and meeting the NEC exit at a roundabout. That's crossing flows.

As for preventing rat running... don't provide any slip roads from Catherine De Barnes Lane at all then and make the village a cul-de-sac. People will still do a circuitous route to avoid the M42 jams.
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Re: M42 Junction 6 improvement

Post by Bryn666 »

darkcape wrote: Tue Sep 04, 2018 20:32 The East dumbbell of M1 J11a was changed during construction to infill the dead bit of roundabout, not sure why it can't be done here. The design team is the same, hence the similarity in junction layout...

The proposed service area is shown as off Solihull Road so unless a major redesign of 5a is expected how will it connect to the motorway? Or (again similar to J11a) the attempts at discouraging rat-running will be undermined by a developer-funded direct connection to the motorway network.
Another example of DMRB being ridiculously gold plated. That infill will have been a Departure.

Yet somehow it makes more sense to have dead carriageway, maintenance burdens, and the rest because "standards".
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Re: M42 Junction 6 improvement

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Alderpoint wrote: Tue Sep 04, 2018 12:07 There have been a few changes (mostly minor) following the consultation earlier this year and further consulation has now opened.

Details here.
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Re: M42 Junction 6 improvement

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This scheme was accepted for examination by the Planning Inspectorate a few days ago. The general arrangement plans are here: https://infrastructure.planninginspecto ... _Plans.pdf

There's an interesting response to public consultation feedback here:
Comment: The biggest concern raised about the Southern Junction is why it is not being designed as a free-flow link, when most of the traffic will be making the movement between the M42 in the south and the new link road. The new link road uses roundabouts with at-grade traffic conflicts seems misconceived, and may result in a decrease in safety.
HE Response: This is noted. The proposed layout has a relatively small footprint. Design development has included realigning the new roundabouts to minimise impact. The dumbbell arrangement also facilitates non-motorway traffic the opportunity to turn around if required. A compact free flow junction design would require greater land take and increased impact on the Scheduled Ancient Woodland.
They don't explain why they're not using a freeflow loop, which would actually take the slip further away from the woodland. And the non-motorway traffic explanation is just weird (they want NMUs going down the new 70mph grade-separated dual carriageway??).

We knew already that there was a rejected octopus/windmill freeflow option (3D). Hidden away in the countless documents I also found a partially-unrolled cloverleaf that was rejected at an early stage:

M42 J6 option 3 - Copy.PNG

You can see the full list of options here:

https://infrastructure.planninginspecto ... ix_4.1.pdf
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Re: M42 Junction 6 improvement

Post by ais523 »

There are no conflicts in the dumbbell design; it's topologically equivalent to a fork junction. You could easily cone off the unused parts of the dumbbell without making any change to the routes people took, and the junction would then be low-speed freeflow (although I suspect this won't happen because the roundabout shape helps to keep HGVs down to a speed where they won't tip over). So I believe this is technically a freeflow junction even without doing that, in the sense that "you never have to stop for conflicting traffic"; it's just not one you can take at 70mph.

I suspect the reason for using a dumbbell rather than a loop is to allow for the northbound slip roads (which were very popular at the consultation) to be easily addable in the future (either for the service station or for relieving congestion at peak times; adding a second route onto the M42 would help avoid queues even if it's a fairly roundabout rout; considerably more roundabout routes, e.g. B4438 northbound, are regularly used for easing congestion, and it seems to be a matter of "get traffic out of the area by any means you can, and it'll find a way to go in its intended direction after that"). Of course, there are environmental reasons not to use a fork.

There's also the possibility of reducing the northbound to westbound footprint of the junction. Having the west roundabout allows that turn to safely be made almost 90 degrees, meaning you lose less woodland on the west side of the junction. I can't see a way to get that sliproad placed that tightly beside the road using a freeflow left, which would have to curve much more gradually. Once you have the west roundabout, there's not much reason not to have the east roundabout too.

Incidentally, the junction is further north of the ideal location (presumably to keep the length of the new road under control). If it ever becomes full-access, it should be 350 metres further south, on the other side of the ancient woodland, to give appropriate weaving space between it and the junctions to the north and south. (HE pretty much outright said to me that the northbound sliproads wouldn't be built unless a service station was also built; northbound sliproads would lead to a minor reduction in safety due to the weaving space being lower than ideal, but the safety benefits of a service station were predicted to outweigh that.)

Now that I'm thinking about this: what about removing the south-facing sliproads from the existing M42 J6, moving the new M42 J5A northwards some distance and making it full access (likely a dumbbell or two-bridge roundabout), adding a freeflow left from the A45 westbound onto the new link road (to the left of the existing freeflow left that goes to the airport), but making it so that traffic turning left off the A45 westbound has to use the roundabout, not the freeflow straight on? This would still allow access to the proposed services (although it would enter the services from a different direction), miss the ancient woodland entirely, be a shorter link (thus less environmentally impactful), reduce the number of traffic conflicts and reduce the number of substandard weaving sections rather than increasing it. I might try to draw this. EDIT: This doesn't work, M42 northbound to the NEC and to the A45 eastbound are too difficult.
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Re: M42 Junction 6 improvement

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^ The turn angle onto the link road from the M42 is gentle (not even half of a right angle) and could easily be freeflow. It only becomes tight in the HE scheme due to deflection for the roundabout.

There are conflicts at the dumbell, e.g. with u-turns (which HE cite as a particular advantage). And even if there weren't, it isn't freeflow if it involves going through give way lines.

They can't move the junction 350m because it isn't on wheels. It's simply in the wrong place, and will always be.

HE want to have their cake and eat it. The documents continually say the north-facing slips and MSA could be added, but that they contravene DMRB weaving requirements. In this way they claim the advantages of the north-facing slips while trying to weasel their way out of the safety implications.

The whole scheme is premised on this sleight of hand. Without it there's no reason to have the dumbbell when a freeflow junction with a loop would have lower impact on the ancient woodland by miving the merge north. And indeed having J5A there at all, with a long link road dangling through greenbelt to reach it, only really makes sense if it's linking to something - the MSA. If you're just trying to take traffic off J6 you'd naturally do that as close to J6 as you can, reducing cost and environmental impact, like every other upgrade of a stackabout (Lofthouse, M62 J6, M25 J2, 10, and 28, etc).
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Re: M42 Junction 6 improvement

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It's still a god awful design. Where do they find these teams to come up with this kind of rubbish?
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Re: M42 Junction 6 improvement

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Just when you think someone has to come their senses regarding free-flow schemes such as Catthorpe and the A14, you get jokes such as this and Wisley.

I don't see the point of changing the existing J6 SB exit loop into the NEC, why go to all that expense just to swap it around? This junction has been tinkered with for years, with HS2 coming it's a good opportunity to sort that whole area out.
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Re: M42 Junction 6 improvement

Post by Truvelo »

jackal wrote: Tue Feb 05, 2019 13:33 We knew already that there was a rejected octopus/windmill freeflow option (3D). Hidden away in the countless documents I also found a partially-unrolled cloverleaf that was rejected at an early stage.
What do the various colours mean on that map? Purple is obvious but the others aren't.
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Re: M42 Junction 6 improvement

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Truvelo wrote: Tue Feb 05, 2019 22:19
jackal wrote: Tue Feb 05, 2019 13:33 We knew already that there was a rejected octopus/windmill freeflow option (3D). Hidden away in the countless documents I also found a partially-unrolled cloverleaf that was rejected at an early stage.
What do the various colours mean on that map? Purple is obvious but the others aren't.
Different options from an early stage:

https://infrastructure.planninginspecto ... %204.1.pdf
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Re: M42 Junction 6 improvement

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darkcape wrote: Tue Feb 05, 2019 22:03 Just when you think someone has to come their senses regarding free-flow schemes such as Catthorpe and the A14, you get jokes such as this and Wisley.

I don't see the point of changing the existing J6 SB exit loop into the NEC, why go to all that expense just to swap it around? This junction has been tinkered with for years, with HS2 coming it's a good opportunity to sort that whole area out.
As I said previously this introduces a flow conflict and actually will increase delays. This is somehow preferable to a 40km/h loop instead of a 50km/h one because DMRB sez.

It's rubbish and smacks of being led by civil engineers rather than traffic ones because it is all formulaic and takes no real world driver behaviour into consideration but neatly ticks all the standards boxes.
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Re: M42 Junction 6 improvement

Post by A303Chris »

Looking at the drawings they show the M42 as 3 lanes with HS north of Junction 6, the current smart motorway arrangement but as 4 lanes ALR south of Junction 6.

Are there proposals to convert the M42 to ALR?
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Re: M42 Junction 6 improvement

Post by Truvelo »

I'm sure someone mentioned on Sabre a while ago it was the intention to convert all hard shoulder running to ALR eventually.
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Re: M42 Junction 6 improvement

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"Additionally, as part of Phase 4 for the Birmingham
Box Smart Motorway programme, consideration
should be given to upgrading the existing Managed
Motorway on the M42 to the newer All Lane
Running standard (where the hard shoulder is
permanently converted into a running lane). A
completed network across the Hub will provide
holistic management and maximise capacity of the
existing assets."

Phase 4 is an RIS2 scheme, i.e. 2020-25. In the same document Midlands Connect propose a longer term widening of J3A-7, presumably to D5M or greater. This is acknowledged in a J6 consultation response:

Consultee comment: "There is a capacity issue on M42
mainline, assume there will be widening
of any structures built to future-proof."
HE response: "This is noted. M42 mainline improvements are outside the scope of the
Scheme – it is noted as a potential future scheme in the Midlands Motorway
Hub Study. Future RIS programmes may include studies to explore corridor
improvements.
Solihull Road overbridge is designed with a span wide enough to futureproof
the structure."

https://www.midlandsconnect.uk/media/12 ... 062018.pdf
https://infrastructure.planninginspecto ... nnex_P.pdf
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Re: M42 Junction 6 improvement

Post by mikehindsonevans »

Funnily enough, we came through this junction this afternoon. The satnav had indicated that the M42 was stuffed from the M40 to j6, so we left the M40 at J15 and bimbled up through Balsall Common, hanging a left onto the A45 and reaching j6.

Her Ladyship was driving and I warned her about the lane markings around the junction. As we crawled out onto the northbound M42, her only comment related to the road designer having been savaged to death by their guide dog!

Surely, the approach of HS2 must give this wretched junction a chance of a proper Catthorpe-style comprehensive rebuild???

Surely?
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Re: M42 Junction 6 improvement

Post by ais523 »

The real problem with the junction complex (Junction 6 itself and the interchanges for the airport and the A452 right next to it) is that there are just way too many main movements. Even apparently major junctions like "one motorway crossing another" have only twelve movements. The junction complex here, though, has something like 28 major movements and a bunch of minor movements (if I've counted correctly, there are 132 possible movements at the junction, and very few of them are completely implausible).
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