A358 Taunton to Southfields

[wrinkly]

As I understand it the whole reason HE is proposing to dual the A358 (which it normally would not consider as it's not a trunk road) is to avoid dualling the corresponding part of the A30/A303.

[jackal]

A quite important point that I missed from the recent announcement is that the whole Taunton to Southfields route will be consulted on, not just the Taunton end as was announced in the summer. This means more radical offline routes like option 1 could potentially be in the mix.

[ChrisH]

A quite important point that I missed from the recent announcement is that the whole Taunton to Southfields route will be consulted on, not just the Taunton end as was announced in the summer. This means more radical offline routes like option 1 could potentially be in the mix.

Presumably this offline route is shorter and therefore gets closer to the A303 in distance? It will be important to make sure this new route is seen as better by routing software, otherwise a lot of drivers will continue to use the A303.

[Richardf]

While it bypasses the worst part of the route the offline option 1 ignores the good quality Hatch Beauchamp bypass completely and cuts through far more unspoilt countryside than other options. At least with a mostly online route you are only affecting a corridor already adversley affected by the existing A358.

I am therefore against Option 1 for those reasons.

[Berk]

While it bypasses the worst part of the route the offline option 1 ignores the good quality Hatch Beauchamp bypass completely and cuts through far more unspoilt countryside than other options. At least with a mostly online route you are only affecting a corridor already adversley affected by the existing A358.

I am therefore against Option 1 for those reasons.

But is that a good enough reason to avoid it?? I think not..

[MotorwayPlannerM21]

I'm worried that all the routes I've seen on here seem to plug directly into the roundabout at Southfields.
Surely this is a foolish place to plug into as it will be difficult to free-flow and still lead to a dogleg in the route?
That's why I propose a free-flow link from the A303 to the A358. I also think the A358 to the south should be re-aligned, avoiding the existing roundabout.

[A320Driver]

While I'm generally in favour of 'new' HQDC being built I don't feel that Option 1 would stack up economically - it wouldn't help with the Yeovil - Taunton flow as much as an online A358 upgrade, and would probably compare less favourably to even upgrading the A303 to Marsh/Honiton in overall environmental terms.

Regarding mapping/sat nav software, I'd imagine that the decrease in journey time and increase in fuel efficiency compared to the A303, along with some forceful signposting plus possibly removing Primary status from the A303 between Ilminster and Honiton, would have the desired effect.

However, I will continue to use the A303 regardless.

[Richardf]

I'm worried that all the routes I've seen on here seem to plug directly into the roundabout at Southfields.
Surely this is a foolish place to plug into as it will be difficult to free-flow and still lead to a dogleg in the route?
That's why I propose a free-flow link from the A303 to the A358. I also think the A358 to the south should be re-aligned, avoiding the existing roundabout.

Earlier plans inclued such a 'cut off' route at the Southfields end. This seems to have been dropped in this 'budget' version of the scheme.

I can see the value of a seperate junction with the M5, that is much further south than the existing one, and I can see merit in an offline route if it is shorter than online, but I don't like the idea of a new road cutting through that area and I can see such a route being harder to get through planning due to local opposition. Whatever the cost differental/advantage, a lengthy planning process might negate that.

[jackal]

I assume a Southfields GSJ would be part of the Ilminster bypass scheme, which is slated for opening in 2028 according to HE documents.

[Richardf]

I assume a Southfields GSJ would be part of the Ilminster bypass scheme, which is slated for opening in 2028 according to HE documents.

Won't be easy to grade seperate Southfields online if the mainline turns a corner!

What if they dual right to Southfields in this scheme, then in the Ilminster scheme they decide to bypass the roundabout to grade separate it? A section of nearly new dual will have to be rebuilt! Better to do something now and future proof the junction for the later upgrade scheme.

[RichardA35]

A quite important point that I missed from the recent announcement is that the whole Taunton to Southfields route will be consulted on, not just the Taunton end as was announced in the summer. This means more radical offline routes like option 1 could potentially be in the mix.

Reading the TAR from the earlier consultation again for the scheme objectives, there is a focus only on the A303/A30 corridor with seemingly little recognition to the regional traffic on the Weymouth/Yeovil - Bristol axis. It will be interesting to see whether HE deal with this or Somerset have to resurrect the Henade Bypass to deal with this or try to mix it all with "local traffic" into the south of Taunton housing/P & R etc development.
It would be nice if HE and a bit of Somerset CC/central DfT thinking and money could be combined and attempt to provide a solution to all the local problems rather than only the minor (in terms of flows at Southfields) A30/A303 corridor.

[jackal]

I doubt it would be quicker to stick to the existing speed restricted route rather than the longer but NSL option 1.

The issue of Henlade needing a separate bypass arguably remains with three of the four shortlisted options (including the consulted option) as the A378 would surely go through there.

[Herned]

The A378 has around 5000 vpd, compared to the best part of 30000 on the A358 through Henlade, so the village will be a very different place even with the A378 traffic going through.

One serious issue with option 1 is the M5 junction layout, it is shown in the technical report as a 270° loop, which doesn't seem a sensible solution for ~3/4 of the current A358 north traffic. I know the junction designs aren't fixed in that report, but it would seem to me that something with much greater land take would be required

[Chris5156]

What if they dual right to Southfields in this scheme, then in the Ilminster scheme they decide to bypass the roundabout to grade separate it? A section of nearly new dual will have to be rebuilt! Better to do something now and future proof the junction for the later upgrade scheme.

I don't see the point in a free-flowing dual carriageway bypassing Southfields only to pile in to a single carriageway road. It's a better and safer transition to have a roundabout interrupt the flow until the next section onwards is dual carriageway too.

Grade separation at Southfields doesn't need to involve a flyover physically passing above the roundabout and making a handbrake 90-degree turn. I'd expect the last half mile or so of A358 and A303 approaching the roundabout to become a set of sliproads and a new curve to be built to the north-east of the roundabout bypassing it completely. The dual carriageway won't be wasted; part would be rebuilt so it would form sliproads meeting the new curve, and the rest would be a pair of two-lane sliproads leading to a major junction, which is not extravagant.

[jackal]

One serious issue with option 1 is the M5 junction layout, it is shown in the technical report as a 270° loop, which doesn't seem a sensible solution for ~3/4 of the current A358 north traffic. I know the junction designs aren't fixed in that report, but it would seem to me that something with much greater land take would be required

There seems to be a bit of a myth that freeflow loops are unsafe or low capacity. DMRB refers to studies that show otherwise, but even so this myth consistently finds its way into UK road schemes, and loops get dropped for less safe and lower capacity two-bridge roundabouts. For recent examples see the A160/A180 redesign and the A14 Bar Hill interchange.

That is absolutely what the alternative is here. Indeed all the other shortlisted options used two bridge roundabouts for that movement.

[Richardf]

What if they dual right to Southfields in this scheme, then in the Ilminster scheme they decide to bypass the roundabout to grade separate it? A section of nearly new dual will have to be rebuilt! Better to do something now and future proof the junction for the later upgrade scheme.

I don't see the point in a free-flowing dual carriageway bypassing Southfields only to pile in to a single carriageway road. It's a better and safer transition to have a roundabout interrupt the flow until the next section onwards is dual carriageway too.

Grade separation at Southfields doesn't need to involve a flyover physically passing above the roundabout and making a handbrake 90-degree turn. I'd expect the last half mile or so of A358 and A303 approaching the roundabout to become a set of sliproads and a new curve to be built to the north-east of the roundabout bypassing it completely. The dual carriageway won't be wasted; part would be rebuilt so it would form sliproads meeting the new curve, and the rest would be a pair of two-lane sliproads leading to a major junction, which is not extravagant.

Could part build or build and half open a GSJ with this scheme and finish or fully open it when the bypass is dualled? That would still control the transition but future proof the junction for the next bit. Less disruption at the junction potentially too.

[Richardf]

What if they dual right to Southfields in this scheme, then in the Ilminster scheme they decide to bypass the roundabout to grade separate it? A section of nearly new dual will have to be rebuilt! Better to do something now and future proof the junction for the later upgrade scheme.

I don't see the point in a free-flowing dual carriageway bypassing Southfields only to pile in to a single carriageway road. It's a better and safer transition to have a roundabout interrupt the flow until the next section onwards is dual carriageway too.

Grade separation at Southfields doesn't need to involve a flyover physically passing above the roundabout and making a handbrake 90-degree turn. I'd expect the last half mile or so of A358 and A303 approaching the roundabout to become a set of sliproads and a new curve to be built to the north-east of the roundabout bypassing it completely. The dual carriageway won't be wasted; part would be rebuilt so it would form sliproads meeting the new curve, and the rest would be a pair of two-lane sliproads leading to a major junction, which is not extravagant.

Could part build or build and half open a GSJ with this scheme and finish or fully open it when the bypass is dualled? That would still control the transition but future proof the junction for the next bit. Less disruption at the junction potentially too.

Edit: How about building the GSJ at Southfields, including a D2 loop for the mainline but opening it as D1? Lane drop/gain where the northern slips join from the roundabout. Temporary tie in with the S2+1 of the bypass.

[JonB2028]

There seems to be a bit of a myth that freeflow loops are unsafe or low capacity. DMRB refers to studies that show otherwise, but even so this myth consistently finds its way into UK road schemes, and loops get dropped for less safe and lower capacity two-bridge roundabouts.

Agree - that's the view espoused here by our safety "expert". Because of procedures like PSCRG (Project Safety Control and Review Group) once that view is established, no matter what the research the standards are based on shows, it is hard to convince people otherwise.

[jackal]

Consultation opens on 16 January.

[WHBM]

Just from casual observation at the M5 roundabout, the principal flow from the A358 appears to be into Taunton. This is quite common, even on trunk roads, that the nearest major centre generates the principal flow. After that, there seems as much turning right, towards Bristol, as left, towards Exeter. This is the signed route from Yeovil, and indeed Weymouth, to Bristol.

Neither of these flows would benefit from a new link to further down the M5.

If the A358 is dualled, I wonder what will be done about the various junctions along the way. Grade separated seems out of fashion. You try even nowadays getting from Hatch Beauchamp village towards Taunton.