A358 Taunton to Southfields

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ikcdab
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Re: A358 Taunton to Southfields

Post by ikcdab »

Herned wrote: Tue Aug 24, 2021 20:25
ikcdab wrote: Tue Aug 24, 2021 18:19 Back in 2002 (approx) there was a suggestion of a second M5 junction which would have taken the A358. That now seems to have disappeared.
I struggle to see how the current plans will improve things. The A358 is currently clogged and at a standstill for most of the day. So what is different now? The new link is clearly designed to take traffic away from the A303 West of ilminster, so even more traffic will be barrelling along the improved A358 and just come to a grinding halt at the j25 signal controlled roundabouts. I see nothing here to ease the standstills on the A358. Am I missing something?
Yes, there will be two lanes for traffic to queue in instead of one! It will also make life more bearable for the residents of Henlade, and no doubt provide lots of lovely development opportunities.

On a more serious note, the works to J25 seem to have reduced the queueing issues a fair bit, even during the very busy holiday season so it might not be too bad, at first. I hope they are safeguarding the land for a direct link to the M5, but I wouldn't count on it
Well I hope you're right! My impression was that the queuing was significantly worse while the works were in hand, and have just reduced back to the pre-works levels.
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jackal
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Re: A358 Taunton to Southfields

Post by jackal »

Apparently they still plan to put in an A358 southbound to M5 northbound segregated left turn, which will be handy, though you have to wonder why it wasn't done with the previous works.

Part of the malignancy of the new roundabout is that it has a SLT for the precious development site traffic, precluding the obvious upgrade of a SLT for A358 northbound to M5 southbound at J25. A lot of thought seems to have gone into bottlenecking the new expressway.
Herned
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Re: A358 Taunton to Southfields

Post by Herned »

jackal wrote: Wed Aug 25, 2021 10:20 Apparently they still plan to put in an A358 southbound to M5 northbound segregated left turn, which will be handy, though you have to wonder why it wasn't done with the previous works.

Part of the malignancy of the new roundabout is that it has a SLT for the precious development site traffic, precluding the obvious upgrade of a SLT for A358 northbound to M5 southbound at J25. A lot of thought seems to have gone into bottlenecking the new expressway.
The pedestrian access to the new business park (if it ever happens), would need to cross any SLT to M5 south so that may be why there isn't one. Not sure there is space to put in one to the northbound carriageway as the roundabout has already been widened, so perhaps that has been superceded?
Herned
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Re: A358 Taunton to Southfields

Post by Herned »

ikcdab wrote: Tue Aug 24, 2021 23:43 Well I hope you're right! My impression was that the queuing was significantly worse while the works were in hand, and have just reduced back to the pre-works levels.
The worst queuing, in the disruptive sense, was traffic heading onto the A358 southbound which frequently blocked back and jammed the roundabout, now that has two lanes for ~500m that shouldn't happen
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jackal
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Re: A358 Taunton to Southfields

Post by jackal »

Herned wrote: Wed Aug 25, 2021 13:45
jackal wrote: Wed Aug 25, 2021 10:20 Apparently they still plan to put in an A358 southbound to M5 northbound segregated left turn, which will be handy, though you have to wonder why it wasn't done with the previous works.

Part of the malignancy of the new roundabout is that it has a SLT for the precious development site traffic, precluding the obvious upgrade of a SLT for A358 northbound to M5 southbound at J25. A lot of thought seems to have gone into bottlenecking the new expressway.
The pedestrian access to the new business park (if it ever happens), would need to cross any SLT to M5 south so that may be why there isn't one. Not sure there is space to put in one to the northbound carriageway as the roundabout has already been widened, so perhaps that has been superceded?
From the Scoping Report (dated 23/3/21):
2.4.3 The proposed scheme would commence at junction 25 of the M5. Modifications to
junction 25 are included as part of the proposed scheme and include a
designated left turn lane from Toneway (Taunton access) onto the M5 northbound
carriageway. Widening is also proposed to southbound M5 off-slip.
As there is already a lane for the left turn, I guess a designated left turn lane means a SLT...

https://infrastructure.planninginspecto ... Report.pdf
Herned
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Re: A358 Taunton to Southfields

Post by Herned »

jackal wrote: Wed Aug 25, 2021 14:32 From the Scoping Report (dated 23/3/21):
2.4.3 The proposed scheme would commence at junction 25 of the M5. Modifications to
junction 25 are included as part of the proposed scheme and include a
designated left turn lane from Toneway (Taunton access) onto the M5 northbound
carriageway. Widening is also proposed to southbound M5 off-slip.
As there is already a lane for the left turn, I guess a designated left turn lane means a SLT...

https://infrastructure.planninginspecto ... Report.pdf
Paragraph 2.4.5 talks about where the scheme reaches the River Tone, so I'm a little bit sceptical about the accuracy of the report
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Chris5156
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Re: A358 Taunton to Southfields

Post by Chris5156 »

ikcdab wrote: Tue Aug 24, 2021 18:19I struggle to see how the current plans will improve things. The A358 is currently clogged and at a standstill for most of the day. So what is different now? The new link is clearly designed to take traffic away from the A303 West of ilminster, so even more traffic will be barrelling along the improved A358 and just come to a grinding halt at the j25 signal controlled roundabouts. I see nothing here to ease the standstills on the A358. Am I missing something?
The volume of traffic on the A358 shouldn't be an issue after the upgrade is completed. It currently carries about 30k vehicles per day, while the A303 through the Blackdown Hills carries 12-15k. Even if the entire traffic load of the A303 transferred on to the new dualled A358 the dual carriageway would cope with it, but of course it won't, because a large slice of the A303 traffic is heading for Honiton or Sidmouth or somewhere else for which the A358 is no use.

The interface between the new dual carriageway and the M5, on the other hand, is an outright embarassment and I won't even pretend to justify it. If the aim is to create a non-stop expressway from M3 J8 to the South West, then stopping it at a signalised roundabout within spitting distance of the M5 (where it will stop again at an already congested roundabout) simply defies all logic.
Herned
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Re: A358 Taunton to Southfields

Post by Herned »

New consultation live this morning. Not read it yet so not sure if there are any new horrors
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jackal
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Re: A358 Taunton to Southfields

Post by jackal »

Plans are much as before, with a grade separated DC crashing into the Nexus 25 roundabout at one end and Southfields at the other.

Regarding the latter it says: "Part of the A358 Taunton to Southfields Dualling
Scheme includes upgrades to the Southfields roundabout so that we can safely adapt it to the new dual carriageway. Although a full upgrade
of the roundabout is not included in these plans, this area of the route is due to be reviewed as part of the A303 Phase 2 upgrade, which is part of the government’s Road Investment Strategy 3 pipeline". As mentioned previously, there is huge flare approaching the roundabout, which looks to me like future proofing, though others may disagree. It is shown well in the video.

There are some segregated left turn antics, with new ones at Southfields and J25 (onto M5nb), and the ridiculous one out of Nexus 25 removed. Unfortunately the opportunity to add a SLT onto M5sb has not been taken. Rather than fiddling with the Nexus 25 roundabout they should have replaced it with a bridge.

General arrangement: https://highwaysengland.citizenspace.co ... 0final.pdf

The dreaded virtual consultation room, including flythrough video: https://a358-taunton-to-southfields.virtual-engage.com/
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Re: A358 Taunton to Southfields

Post by Herned »

The scheme looks fine, apart from the joke that is J25. I have filled in the consultation form and made clear that I think it is stupid, and at the very least hope they have safeguarded the route for the wb direct link to the M5. It is astonishing (or not), that they are planning on widening the link between the two roundabouts even though it opened this year!

I don't see that the flaring at Southfields can be for anything other than a future flyover to the A303, it's even more pronounced in the video than the drawings. I might go and ask at the consultation
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Re: A358 Taunton to Southfields

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Herned wrote: Tue Oct 12, 2021 12:27The scheme looks fine, apart from the joke that is J25. I have filled in the consultation form and made clear that I think it is stupid, and at the very least hope they have safeguarded the route for the wb direct link to the M5.
I've also filled in the consultation and said much the same. The idea that billions will be spent making a continuous expressway on the A303 and A358, including the Stonehenge Tunnel and all sorts of dualling work to get rid of the bottlenecks, only for it to come to a stop at a roundabout within sight of the M5, just beggars belief. How qualified highway engineers could propose it with a straight face I don't know.
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JammyDodge
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Re: A358 Taunton to Southfields

Post by JammyDodge »

Herned wrote: Tue Oct 12, 2021 12:27 The scheme looks fine, apart from the joke that is J25. I have filled in the consultation form and made clear that I think it is stupid, and at the very least hope they have safeguarded the route for the wb direct link to the M5. It is astonishing (or not), that they are planning on widening the link between the two roundabouts even though it opened this year!
I think that the majority on here think it is very very dumb for it not to be done from the get go. But hey, that is the British way. Looking at the plans for Nexus 25, it seems that safeguarding will be relatively easy, if this plan is correct, then this would be a possible solution
Screenshot 2021-10-13 0336310.jpg
Herned wrote: Tue Oct 12, 2021 12:27 I don't see that the flaring at Southfields can be for anything other than a future flyover to the A303, it's even more pronounced in the video than the drawings. I might go and ask at the consultation
Agreed. If the fly-through is correct, then there is little doubt about this being for a flyover. It may also be the case, that when a flyover is built, an entirely new junction will be built to link to the existing roundabout
Screenshot 2021-10-13 032719.jpg
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Herned
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Re: A358 Taunton to Southfields

Post by Herned »

JammyDodge wrote: Wed Oct 13, 2021 03:43 I think that the majority on here think it is very very dumb for it not to be done from the get go. But hey, that is the British way. Looking at the plans for Nexus 25, it seems that safeguarding will be relatively easy, if this plan is correct, then this would be a possible solution
Screenshot 2021-10-13 0336310.jpg
Unfortunately there is no way that would be possible, the angles and vertical distances are far too severe. The link roads were planned to go further south, allowing much smoother curves and higher speeds.

On second thoughts, physically it would probably be possible to have much tighter turns and higher gradients, but the rules wouldn't allow it. Pragmatism is dead
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ChrisH
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Re: A358 Taunton to Southfields

Post by ChrisH »

The M5 end of this is a complete bin fire. Not only are they not doing it properly, there is no provision to come back and do it properly in the future. My consultation response says so.
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Re: A358 Taunton to Southfields

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JammyDodge wrote: Wed Oct 13, 2021 03:43 Screenshot 2021-10-13 032719.jpg
A botched sign before the road is even built! The destinations on the A303 shouldn't be on white patches.
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Re: A358 Taunton to Southfields

Post by Truvelo »

SouthWest Philip wrote: Wed Oct 13, 2021 18:55
JammyDodge wrote: Wed Oct 13, 2021 03:43 Screenshot 2021-10-13 032719.jpg
A botched sign before the road is even built! The destinations on the A303 shouldn't be on white patches.
I noticed that but this is the secondary sign showing the local destinations. Does this still apply?
How would you like your grade separations, Sir?
Big and complex.
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Chris5156
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Re: A358 Taunton to Southfields

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Truvelo wrote: Wed Oct 13, 2021 19:16
SouthWest Philip wrote: Wed Oct 13, 2021 18:55
JammyDodge wrote: Wed Oct 13, 2021 03:43 Screenshot 2021-10-13 032719.jpg
A botched sign before the road is even built! The destinations on the A303 shouldn't be on white patches.
I noticed that but this is the secondary sign showing the local destinations. Does this still apply?
It does - if the road is primary all the signs pointing down it should be in primary colours.
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Re: A358 Taunton to Southfields

Post by TimM3-A55 »

To me the 'bin fire' at the M5 junction is due to the differences in what this scheme is sold as (part of the expressway to the southwest) with what the A358 actually does. More traffic from A358 heads over the roundabout and continues into Taunton, as does traffic leaving Taunton. Traffic flows A358 - M5(S) and M5(N) - A 358 as some of the lowest at J25, in total more head to/from the M5(N). Turning movements posted here.

This goes back to whether the A358 is a viable alternative to the A303/A30 Black down hills to complete the expressway to the southwest. To me it isn't, I will still use the A303/A30 Black down hills, I don't think I'm alone in thinking that. However, the A358 is a much needed upgrade for both local traffic and long distance traffic, more needed than upgrading the A303/A30 Black down hills and even much of the S2 A303. To avoid the minefield of upgrading the A303/A30 Black down hills upgrading the A358 has been pitched as an alternative. There isn't really a problem with this, it gets the A358 upgraded and, by extension, the A303. But all the upgrades to J25 have had to give priority to "expressway to southwest" traffic and in all proposed cases to detriment of other traffic movements. One option had a new full access junction south of J25, others left the A358 single approaching the current M5 junction with a new free flow fork on the M5. All of these would do nothing for traffic entering/leaving Taunton on the A358, or traffic to/from the M5(N). Some would probably have made these movements worse. What's needed is free flow links into Taunton and to/from the M5(N), but these don't fit in with the expressway to the southwest project. I really think what has just been proposed is the best we are going to get.

I came up the bellow/attached idea sometime ago (before nexus 25 appeared) using the M40/A46 junction as a starting point. Requires bulldozing the Sainsburys and most of the rest of the retail park. It's not particularly well drawn but good enough to show the idea I think. I'm sure the loop is far too tight, I guess it could be made bigger by curving/bending the new flyover to the north. The B&Q and Halfords would have to go to make that roundabout bigger. Even without the loop just taking A358 through traffic away from the J25 roundabout would help a lot.
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Herned
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Re: A358 Taunton to Southfields

Post by Herned »

TimM3-A55 wrote: Sat Oct 16, 2021 17:09 I came up the bellow/attached idea sometime ago (before nexus 25 appeared) using the M40/A46 junction as a starting point. Requires bulldozing the Sainsburys and most of the rest of the retail park. It's not particularly well drawn but good enough to show the idea I think. I'm sure the loop is far too tight, I guess it could be made bigger by curving/bending the new flyover to the north. The B&Q and Halfords would have to go to make that roundabout bigger. Even without the loop just taking A358 through traffic away from the J25 roundabout would help a lot.
That's ambitious, to say the least. I can't help wondering if knocking down £50m+ worth of property might present a little bit of an issue with the business case.

That said, it does make a lot of sense to prioritise the straight-on movement across the junction. I have vaguely considered that a single carriageway flyover like the one at Penn Inn on the A380 might be possible, flying over all three roundabouts and the M5. There is space to do it, in theory
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Re: A358 Taunton to Southfields

Post by Phil »

TimM3-A55 wrote: Sat Oct 16, 2021 17:09 To me the 'bin fire' at the M5 junction is due to the differences in what this scheme is sold as (part of the expressway to the southwest) with what the A358 actually does. More traffic from A358 heads over the roundabout and continues into Taunton, as does traffic leaving Taunton. Traffic flows A358 - M5(S) and M5(N) - A 358 as some of the lowest at J25, in total more head to/from the M5(N). Turning movements posted here.

This goes back to whether the A358 is a viable alternative to the A303/A30 Black down hills to complete the expressway to the southwest. To me it isn't, I will still use the A303/A30 Black down hills, I don't think I'm alone in thinking that. However, the A358 is a much needed upgrade for both local traffic and long distance traffic, more needed than upgrading the A303/A30 Black down hills and even much of the S2 A303. To avoid the minefield of upgrading the A303/A30 Black down hills upgrading the A358 has been pitched as an alternative. There isn't really a problem with this, it gets the A358 upgraded and, by extension, the A303. But all the upgrades to J25 have had to give priority to "expressway to southwest" traffic and in all proposed cases to detriment of other traffic movements. One option had a new full access junction south of J25, others left the A358 single approaching the current M5 junction with a new free flow fork on the M5. All of these would do nothing for traffic entering/leaving Taunton on the A358, or traffic to/from the M5(N). Some would probably have made these movements worse. What's needed is free flow links into Taunton and to/from the M5(N), but these don't fit in with the expressway to the southwest project. I really think what has just been proposed is the best we are going to get.

You miss the point. Removing M5 - A358 traffic would take it off the roundabout leaving more space for traffic heading elsewhere.

Go and have a look across Europe and you find they build lots of S2 flyovers or GSJs on S2 roads precisely because it eases the load on other flows - were as here we plonk in a roundabout then signalise it!

As for Taunton - M5 north free flow -knocking down large amounts of property (even if it is tin sheds) is going to be a complete non starter both due to cost and political pressure from the businesses themselves - but HE / NH had the opportunity to provide a free flow A358 - M5 option without any demolition which would have at least removed that traffic from the equation. Instead we have an otherwise excellent road improving being ruined by penny pinching / pandering to ruinous 'development must be facilitated' mentality
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