M42 Junction 6 improvement

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jackal
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Re: M42 Junction 6 improvement

Post by jackal »

The consultation is open. Nothing much has changed since the PRA in August.

https://highwaysengland.citizenspace.co ... sultation/
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mapboy
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Re: M42 Junction 6 improvement

Post by mapboy »

If it wasn't clear before why the new southern junction isn't free flow then it is now. As we expected, it has been designed to allow the proposed service station to plug into the western roundabout of the dumbbell.
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jackal
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Re: M42 Junction 6 improvement

Post by jackal »

It doesn't really explain the eastern roundabout, which will still be useless when the service station is plugged into the western one.

With north-facing slips apparently discounted, access to the service station to/from the M42 north will presumably be via the stackabout and Clock interchange, adding congestion to not one but three junctions...
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Re: M42 Junction 6 improvement

Post by tom1977 »

jackal wrote:It doesn't really explain the eastern roundabout, which will still be useless when the service station is plugged into the western one.

With north-facing slips apparently discounted, access to the service station to/from the M42 north will presumably be via the stackabout and Clock interchange, adding congestion to not one but three junctions...
Unless the developer builds the missing slip roads. Are they in the planning application?
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Re: M42 Junction 6 improvement

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I've been to the consultation that was hosted today.

I asked several questions about the new junction (and its odd "half-dumbbell" appearance), and was told quite a bit of information that isn't immediately apparent from the plans. Based on what I heard, it's basically designed like that for two reasons: a) to work either with or without the service station, b) to handle some environmental constraints on the area.

In terms of a), it seems that there isn't enough room to put in a full motorway-junction-standard slip road to the north of the junction without causing unacceptable weaving issues (there is to the south, just about). However, apparently the safety issues that would result from putting in lower-standard sliproads (of the sort normally used for service stations) would be outweighed by the safety benefits of a service station in the area. My understanding from the consultation is that HE has no objection to slip roads being built to connect the junction to the motorway to/from the north, if and only if there's a service station there to offset the issues caused by the weaving. Note that there's still a substandard distance from the new junction to the existing J6, but this was the case even with the original service station plans (i.e. there's no change here from what was seen in the original plans for the service station).

In terms of b), it seems that there are environmental constraints that prevent a skew bridge being built across the motorway (i.e. the bridge has to cross at close to 90 degrees). This makes the right turn onto the motorway slip road (for traffic coming from Clock Interchange towards the M42 southbound) too sharp to negotiate at anything like full speed (it's more than 90 degrees and has a tiny radius). HE decided that a pair of roundabouts, one just before and one at the extremely sharp turn, would be likely to be beneficial in terms of preventing accidents as a consequence of overspeeding, as most traffic already knows how to behave at a roundabout. Note that with the proposed design, there are no conflicts at either roundabout (barring the extremely unlikely situation of vehicles doing a U-turn there). The situation here was explained to me along the lines of "there's probably more than one way to deal with the safety issue of the right turn onto the M42 southbound, but we picked this one because it's compatible with the service station and works even without it".
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Re: M42 Junction 6 improvement

Post by Truvelo »

I suppose another advantage of the dumbbell is it removes the need for the link to Clock Interchange to be motorway as the roundabouts allow prohibited traffic to turn round.
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jackal
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Re: M42 Junction 6 improvement

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They could use a loop, i.e. drivers cross the M42, turn left 270 degrees, and merge with the M42sb. But it would make it harder to plug in the service station.

Even if the service operator ends up paying for the north facing slips, they presumably won't be paying the far greater cost for the rest of the interchange, though it is essentially built for their benefit. One of many things that doesn't smell right about this scheme.
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Re: M42 Junction 6 improvement

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jackal wrote:They could use a loop, i.e. drivers cross the M42, turn left 270 degrees, and merge with the M42sb. But it would make it harder to plug in the service station.

Even if the service operator ends up paying for the north facing slips, they presumably won't be paying the far greater cost for the rest of the interchange, though it is essentially built for their benefit. One of many things that doesn't smell right about this scheme.
I suspect that this is actually one of the cheapest interchange designs available. A loop would be considerably more expensive in landtake, at least, and the cost of a couple of roundabouts is likely to be negligible by comparison.
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Re: M42 Junction 6 improvement

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Cheap for the taxpayer, compared to the MSA operator paying for it, as I believe was originally planned? Cheap compared to not building it or the link road at all?

£328.7m is not a small amount of money, and would deliver much more were it actually focused on improving J6 rather than corporate welfare.
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Re: M42 Junction 6 improvement

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I mean, this is one of the cheapest ways to build the new link road, assuming that you want to build it. (And the link road is one of the cheapest ways to improve J6, other than the freeflow lefts which are also being built.)

Are you implying that you think that the current solution isn't fit for purpose and one of the other options would have been better, with the link road put there purely for the benefit of the MSA? I'd argue that pretty much the exact opposite is the case: HE were trying hard to avoid having to put a junction there (at least partly because the environmentalists would have been much happier with an extra junction to the north instead), but it turned out to be the only viable option.

(Additionally, I strongly suspect that the new half-dumbbell is a fairly minor cost compared to the cost of the rest of the scheme; in fact, designing it in a way that's compatible with the existing plans by third parties probably actually makes it cheaper. This junction isn't being built for the benefit of the MSA proposal. It's being built for the benefit of M42 J6 and the A45.)
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Re: M42 Junction 6 improvement

Post by darkcape »

£330m seems a massive amount of money for a scheme with a handful of bridges and 1.5km of road.

I used to commute to the airport a few years ago before the A45 was widened, and although it'd be busy it would only get very busy in the evening rush hour, heading from the A45 eastbound up the slip to the J6 island. So I'm not sure how much this is going to improve flow around the island.

The road arrangements around there are already a bit of a mess - Clock, J6 and Stonebridge are in very close proximity, the A452 and M42 to the north is having major work as part of HS2. The whole area needed a good look at and rebuilding e.g. collector/distributor slips between J6 and Clock. An opportunity was missed when the A45 was widened (and potentially when the runway extended and diversion) over the WCML to sort this out better. I feel that all this will do is snarl up the Clock interchange and shift the problem half a kilometre to the west.

Surely for £330m we could have better - with this and the A3/M25 it seems a lot of money being spent for little major improvement.
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Re: M42 Junction 6 improvement

Post by Truvelo »

I suggested a link to the B4102 before but the idea was refuted as it would result in Hampton in Arden becoming a ratrun to the M42.

How about this layout? This makes the new junction freeflow between the M42 and Clock Interchange. The connection to the B4102 doesn't allow any access to the M42 so no ratrunning through the village. It will dramatically decrease traffic using Shadowbrook Lane.
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Re: M42 Junction 6 improvement

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ais523 wrote:Are you implying that you think that the current solution isn't fit for purpose and one of the other options would have been better
Yes, exactly that. Here are the pricings from the TAR:

2K Southern Junction alternative £272m
3D Interchange option £441m

2K is what was subsequently developed into the preferred route.

3D is the full freeflow rebuild of J6. It would be a long term solution that would transform all movements at J6, instead of a short term, dangerous bodge that takes only one movement off J6 - and even that faces multiple roundabouts.

But don't take my word for it. As the SAR explains, the preferred option has 'an increase in the number of conflict points associated with the introduction of additional roundabout junctions, which also gives rise to a predicted increase in accident numbers' (p. 46). It is actually projected to result in 133 additional casualties during the assessment period.

An absolute joke of a scheme.
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Re: M42 Junction 6 improvement

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jackal wrote:
ais523 wrote:Are you implying that you think that the current solution isn't fit for purpose and one of the other options would have been better
Yes, exactly that. Here are the pricings from the TAR:

2K Southern Junction alternative £272m
3D Interchange option £441m

2K is what was subsequently developed into the preferred route.

3D is the full freeflow rebuild of J6. It would be a long term solution that would transform all movements at J6, instead of a short term, dangerous bodge that takes only one movement off J6 - and even that faces multiple roundabouts.

But don't take my word for it. As the SAR explains, the preferred option has 'an increase in the number of conflict points associated with the introduction of additional roundabout junctions, which also gives rise to a predicted increase in accident numbers' (p. 46). It is actually projected to result in 133 additional casualties during the assessment period.

An absolute joke of a scheme.
A full rebuild would cause massive disruption during construction. I imagine JLR would lobby hard against such a proposal. In fact, I imagine they are lobbying hard for HE to build the southern junction with four slip roads so that they have an additional route for their traffic past the MSA which they will use as a lorry park.
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Re: M42 Junction 6 improvement

Post by Bryn666 »

Disruption there may be, and there was certainly disruption in several US examples when inadequate interchanges were built from scratch, but you sometimes need to accept a dose of pain to get a cure.
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Re: M42 Junction 6 improvement

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Jackal wrote:But don't take my word for it. As the SAR explains, the preferred option has 'an increase in the number of conflict points associated with the introduction of additional roundabout junctions, which also gives rise to a predicted increase in accident numbers' (p. 46). It is actually projected to result in 133 additional casualties during the assessment period.
Wait, they're proposing building something their own research says will increase collisions and casualties? What cretin signed off on that one then, and where can the rest of us ensure we never do business with them?

I bet the Stage 1 RSA has had a field day with this.

It's a given that a new junction may cause a shift in causation of casualties, e.g. a roundabout being converted to signals will introduce new conflict points where there were previously none, but I am not aware of any scheme ever saying it will actively make safety worse yet being allowed to go ahead.
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Re: M42 Junction 6 improvement

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It's right there in the SAR, starting at page 45. They do try to fudge it a bit by saying that 'a separate safety assessment' for the strategic network around J6 showed they could introduce accident-reducing measures, and if you combine the effects of those with this scheme (option 1) there is a net reduction in accidents. So I suppose that's why they think they've cleared the safety hurdle. But the report is clear that the scheme itself reduces safety.
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Re: M42 Junction 6 improvement

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Thanks for the link, I had a look earlier from where you previously showed it. They anticipate approximately 2 casualties per year increase as part of this scheme over their 60 year assessment period.

Despite the fudge there is no good news from that. The proposed link road is going to be, by its very nature, congested. Introducing at-grade conflicts along its route is therefore a poor decision that will be regretted further down the line, especially once the local authorities decide that it's ripe for development.

The constraints seem to be the following, and none of them are exactly insurmountable despite requiring political backbone:

1. The SSSI. Probably best to leave this intact given the amount of urbanisation in the area (which will be massively worsened by HS2). The link road as proposed only just dodges it.
2. The Motorcycle Museum. How expensive would it be to relocate this, in all seriousness? It isn't as if it is in a significant building; it's relatively new.
3. The existing junction. The worst of the problems to overcome, but still doable.

I would argue a free-flow solution, even with reduced specification than the rejected option (the rest of Europe copes with low speeds on interchange connectors if need be), would still be the best solution long term.
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Re: M42 Junction 6 improvement

Post by darkcape »

I would've thought the M42 Nb to A45 WB movement, whilst already catered for, could be built a lot closer to the junction say running parallel to the rail line. The reverse movement could be built by a viaduct over J6, nicking some car park land from the NEC in the NW quadrant. They did it with the M25/A2. And built viaducts over an existing motorway junction at M1 J19.
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Re: M42 Junction 6 improvement

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Bryn666 wrote:Introducing at-grade conflicts along its route is therefore a poor decision that will be regretted further down the line, especially once the local authorities decide that it's ripe for development.
Wait, what at-grade conflicts?

There were some in earlier versions of the plans (in which the connections between the link road and B4438 were at-grade rather than grade-separated like they are in this version), but I don't believe the current plans introduce any new conflicts anywhere along the link road or the junction between the motorway and link road (and the intention is to signalise Clock Island, meaning that there'll be no conflicts there either unless someone jumps the lights).
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