A358 Taunton to Southfields

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jackal
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Re: A358 Taunton to Southfields

Post by jackal » Sun Oct 17, 2021 08:28

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.
I'd put in a flyover online, as I sketched a few years ago. There should be space without demolishing any buildings, though adjacent land is required. I've drawn these slips the same size as the M5 ones - in fact they could be made significantly smaller if necessary using retaining walls and a lower quality alignment. The northbound merge would have to be signalised in any case.

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Re: A358 Taunton to Southfields

Post by DavidBrown » Sun Oct 17, 2021 09:28

I'm not sure where any rationale is for a freeflow A358 into Taunton link? It crashes straight into another roundabout 200 yards up the road, and a traffic signal crossroads a few hundred yards beyond that. Given you've already got Blackbrook and soon to be Nexus dumping local traffic straight onto the J25 roundabout, it makes sense to keep that for local traffic only, and remove longer distance traffic by providing new A358-M5 movements elsewhere.

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Re: A358 Taunton to Southfields

Post by SteveA30 » Sun Oct 17, 2021 09:57

I'll be going to the consultation at Monks yard, Ilminster on Sat Oct 23, 11am-6pm, to give them a piece of my mind (the top left corner). They must know the J25 plan is rubbish so what is the real underlying behind the scenes reason why it is proposed?

https://monksyard.co.uk/ This is in the Secret Services thread, on the old A358 next to the old A303 but still the A358..... bit.
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jackal
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Re: A358 Taunton to Southfields

Post by jackal » Sun Oct 17, 2021 12:48

DavidBrown wrote:
Sun Oct 17, 2021 09:28
I'm not sure where any rationale is for a freeflow A358 into Taunton link? It crashes straight into another roundabout 200 yards up the road, and a traffic signal crossroads a few hundred yards beyond that. Given you've already got Blackbrook and soon to be Nexus dumping local traffic straight onto the J25 roundabout, it makes sense to keep that for local traffic only, and remove longer distance traffic by providing new A358-M5 movements elsewhere.
As mentioned above an A358 flyover would reflect the traffic volumes. M5 (south) to/from A358 (east) is a minor pair of movements by comparison:


Image


Anyway, my main point is that some freeflow to take a significant amount of traffic off the roundabout is required - if not M5 to A358 then A358 to A358.

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Re: A358 Taunton to Southfields

Post by hoagy_ytfc » Sun Oct 17, 2021 23:31

SteveA30 wrote:
Sun Oct 17, 2021 09:57
I'll be going to the consultation at Monks yard, Ilminster...

Well that's a bit weird - I'd never heard of Monks Yard so I followed the link, and...

It turns out I worked in that building a while back when it was occupied by a software company.

I'm sure you all needed to know that...

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Re: A358 Taunton to Southfields

Post by the cheesecake man » Mon Oct 18, 2021 13:28

jackal wrote:
Sun Oct 17, 2021 12:48

Image
Why do 9 people leave the M5 southbound and rejoin? Why does noone travelling northbound do that? :coat:

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Re: A358 Taunton to Southfields

Post by boliston » Mon Oct 18, 2021 23:26

jackal wrote:
Sun Oct 17, 2021 08:28
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.
I'd put in a flyover online, as I sketched a few years ago. There should be space without demolishing any buildings, though adjacent land is required. I've drawn these slips the same size as the M5 ones - in fact they could be made significantly smaller if necessary using retaining walls and a lower quality alignment. The northbound merge would have to be signalised in any case.

Image
i would imagine having a flyover to connect local taunton traffic with the new dualled a358 would have to be very high considering the m5 is already a lot higher than the a358 - expect the bulk of people leaving taunton will be aiming to get onto the m5 rather than go across it in the direction of ilminster

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Re: A358 Taunton to Southfields

Post by Herned » Tue Oct 19, 2021 09:02

boliston wrote:
Mon Oct 18, 2021 23:26
i would imagine having a flyover to connect local taunton traffic with the new dualled a358 would have to be very high considering the m5 is already a lot higher than the a358 - expect the bulk of people leaving taunton will be aiming to get onto the m5 rather than go across it in the direction of ilminster
The real (if outdated) turning figures for the junction are listed a couple of posts above - the movements along the A358 across the junction is, just, the biggest flow. I wouldn't have thought that either but the numbers are there

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Re: A358 Taunton to Southfields

Post by Richardf » Tue Oct 19, 2021 23:07

Couldn't the A358 into Taunton go through the roundabout? Much cheaper than a flyover or offline bypass? Roundabout is signalised anyway so wouldn't make much difference in that respect.

Maybe then some sort of limited freeflow links to the M5 could be fitted in?
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Re: A358 Taunton to Southfields

Post by A320Driver » Wed Oct 20, 2021 11:35

The issue at this junction is it serves (or will serve) basically three purposes:

1 - major access into Taunton from M5
2a - M5-A358-A303 flow
2b - M5-A358-Yeovil and south coast flow
3 - local traffic

As such it will be a disaster from day one. The A358 needs to be taken to the south with its own junction 25A, that’s the only viable solution.
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Re: A358 Taunton to Southfields

Post by Peter350 » Wed Oct 20, 2021 15:07

A320Driver wrote:
Wed Oct 20, 2021 11:35
The issue at this junction is it serves (or will serve) basically three purposes:

1 - major access into Taunton from M5
2a - M5-A358-A303 flow
2b - M5-A358-Yeovil and south coast flow
3 - local traffic

As such it will be a disaster from day one. The A358 needs to be taken to the south with its own junction 25A, that’s the only viable solution.
The thing is that unless a lot of South West traffic is willing to divert away from the Blackdown Hills, any freeflow A358 to M5 South will likely be less busy than most other movements that have to use the roundabout. J25 is the only decent access to Taunton from pretty much anywhere else in the country, and as such the only way to relieve it is to build another junction to serve the town. I’m thinking you could have a set of north-facing slip roads just north of J25 to link up with Heron Gate (the unclassified road serving the retail park), which achieves the objective of separating Taunton - M5 north traffic from the A358.

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Re: A358 Taunton to Southfields

Post by jackal » Wed Oct 20, 2021 15:39

Peter350 wrote:
Wed Oct 20, 2021 15:07
The thing is that unless a lot of South West traffic is willing to divert away from the Blackdown Hills...
Let's just pause to consider that NH are building a half billion pound expressway for the specific purpose of taking vehicles away from a sparsely trafficked rural A road, and to a heavily congested urban motorway junction...

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Re: A358 Taunton to Southfields

Post by Peter350 » Wed Oct 20, 2021 15:49

jackal wrote:
Wed Oct 20, 2021 15:39
Peter350 wrote:
Wed Oct 20, 2021 15:07
The thing is that unless a lot of South West traffic is willing to divert away from the Blackdown Hills...
Let's just pause to consider that NH are building a half billion pound expressway for the specific purpose of taking vehicles away from a sparsely trafficked rural A road, and to a heavily congested urban motorway junction...
Just because NH (nee HE) are proposing to route traffic onto this new expressway won’t necessarily mean drivers will do so in practice. Unless signage and sat-nav data is changed to favour the A358, traffic will continue to use the A303 Blackdown Hills route.

Moreover, if you’re intending to divert all strategic A303 traffic via the A358, you really need to do it properly. By that I mean full freeflow at Southfields and onto the M5(S).

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Re: A358 Taunton to Southfields

Post by Herned » Wed Oct 20, 2021 16:21

Peter350 wrote:
Wed Oct 20, 2021 15:49
Just because NH (nee HE) are proposing to route traffic onto this new expressway won’t necessarily mean drivers will do so in practice. Unless signage and sat-nav data is changed to favour the A358, traffic will continue to use the A303 Blackdown Hills route.

Moreover, if you’re intending to divert all strategic A303 traffic via the A358, you really need to do it properly. By that I mean full freeflow at Southfields and onto the M5(S).
I would be amazed if the signs aren't updated in favour of the A358 route. Sat navs will route according to user preference and journey time, if you have it set for fastest journey and/or highest quality roads then you will be directed via the A358. It's ~9 miles more, which should be noticeably quicker from Ilminster to Exeter.

But of course your second point is absolutely right, and will have a big bearing on whether or not the fastest route is via the A358

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Re: A358 Taunton to Southfields

Post by jackal » Wed Oct 20, 2021 17:11

Herned wrote:
Wed Oct 20, 2021 16:21
Peter350 wrote:
Wed Oct 20, 2021 15:49
Just because NH (nee HE) are proposing to route traffic onto this new expressway won’t necessarily mean drivers will do so in practice. Unless signage and sat-nav data is changed to favour the A358, traffic will continue to use the A303 Blackdown Hills route.

Moreover, if you’re intending to divert all strategic A303 traffic via the A358, you really need to do it properly. By that I mean full freeflow at Southfields and onto the M5(S).
I would be amazed if the signs aren't updated in favour of the A358 route.
Given the design at J25 it would be better if they weren't. The scheme makes much more sense if you look at it purely as relief for the congested single carriageway A358, with Exeter traffic continuing to use the A30/A303.

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Re: A358 Taunton to Southfields

Post by Dan Lockton » Wed Oct 20, 2021 17:38

Just because NH (nee HE) are proposing to route traffic onto this new expressway won’t necessarily mean drivers will do so in practice. Unless signage and sat-nav data is changed to favour the A358, traffic will continue to use the A303 Blackdown Hills route.
I wonder whether the A303 (and A30) between the A358 and Honiton would remain primary, or not? Or even renumbering the A358 to A303? That might make a difference to how it's perceived on maps and on the ground, even if only by people who don't just automatically continue on the route they've always known. This is what I imagine it might look like, but would it make any difference? (other than to who maintains it) Image
(oh, the image didn't work: here's a link http://danlockton.co.uk/images/A30-A303-v4.jpg )

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Re: A358 Taunton to Southfields

Post by Herned » Wed Oct 20, 2021 19:24

jackal wrote:
Wed Oct 20, 2021 17:11
Given the design at J25 it would be better if they weren't. The scheme makes much more sense if you look at it purely as relief for the congested single carriageway A358, with Exeter traffic continuing to use the A30/A303.
Yes, agreed, but even so, the project pages have always referred to it as "part of a long term aim to create a high-quality dual carriage way link between London and the South East and the South West". Which strongly suggests they intend it to be the strategic route

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Re: A358 Taunton to Southfields

Post by Truvelo » Wed Oct 20, 2021 20:58

Dan Lockton wrote:
Wed Oct 20, 2021 17:38
Just because NH (nee HE) are proposing to route traffic onto this new expressway won’t necessarily mean drivers will do so in practice. Unless signage and sat-nav data is changed to favour the A358, traffic will continue to use the A303 Blackdown Hills route.
I wonder whether the A303 (and A30) between the A358 and Honiton would remain primary, or not? Or even renumbering the A358 to A303? That might make a difference to how it's perceived on maps and on the ground, even if only by people who don't just automatically continue on the route they've always known. This is what I imagine it might look like, but would it make any difference? (other than to who maintains it) Image
(oh, the image didn't work: here's a link http://danlockton.co.uk/images/A30-A303-v4.jpg )
That is a great map. Looking at it closely suggests the time taken to travel via the upgraded A358 could well be less than the existing Blackdown route even though it's a longer distance. If the existing route was downgraded to non primary then it would appear to be a no brainer when looking at a map. On the flip side if enough traffic transfers to the A358 route then the Blackdown route would be quicker than it is at present if one can cruise at a higher average speed with less traffic to get in the way. Despite all this I still believe the abandoned plans of 30 years ago would have been the best solution along with an upgraded A358 giving two dualled routes between Ilminster and the M5.
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Re: A358 Taunton to Southfields

Post by AAndy » Sat Oct 23, 2021 08:35

I doubt the M5 could cope with integrating the a303, it is past capacity most waking parts of days during the summer.

What is needed is a viable alternative to the M4/M5 route from London to Exeter which is the 303.

Blackdown does not need dualling, but would benefit from redesign junctions for joining roads even gsj for the b roads and lights, and straightening of some sections.

fwiw I use other routes instead of the A303 & M5 during the daytime which either route through Blandford if travelling East or Bath if travelling north or to wales.

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Re: A358 Taunton to Southfields

Post by WHBM » Sat Oct 23, 2021 09:14

Peter350 wrote:
Wed Oct 20, 2021 15:49

Just because NH (nee HE) are proposing to route traffic onto this new expressway won’t necessarily mean drivers will do so in practice. Unless signage and sat-nav data is changed to favour the A358, traffic will continue to use the A303 Blackdown Hills route.
I know the roads in the area, as I suspect the bulk of any area traffic flow does. I don't need a Satnav. But I would certainly continue to go from the A303 via Honiton if heading for Exeter and beyond. If nothing else the road on from Honiton to Exeter is a glorious dual carriageway.

Has there ever been such a dog-leg reroute anywhere else that has succeeded ?

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