A358 Taunton to Southfields

[Herned]

I have given the turning figures a few posts above (minus car/HGV split).

Yes, and thanks for that, but I did mean with the splits

[Richardf]

If they want traffic to go up the A358 then the A303/358 junction needs to prioritise this route instead of the A303. Whether this is done by bypassing the junction and making the desired route the mainline or by cheaper methods like signage or alterations to the existing roundabout will depend on budgets and will to do it. But unless something like this is done, traffic will probably still want to take what appears to be the more direct or shorter route, regardless of the road standard.

Satnavs will also play a role here. They tend to offer either the shortest abd/or fastest route. There will be occasions when the M5 is busy and it might actually be quicker to go A303/A30, which to a Satnav will also be the shortest route.

[WHBM]

Interesting figures, thank you. By far the biggest flows are to/from Taunton town, rather than any longer distance ones.

Which is both intuitively what I expected, and also what would be standard in such a situation.

[Berk]

If they want traffic to go up the A358 then the A303/358 junction needs to prioritise this route instead of the A303. Whether this is done by bypassing the junction and making the desired route the mainline or by cheaper methods like signage or alterations to the existing roundabout will depend on budgets and will to do it. But unless something like this is done, traffic will probably still want to take what appears to be the more direct or shorter route, regardless of the road standard.

There was a suggestion that Southfields roundabout could be bypassed as part of either this scheme, or the Ilminster bypass dualling.

Satnavs will also play a role here. They tend to offer either the shortest abd/or fastest route. There will be occasions when the M5 is busy and it might actually be quicker to go A303/A30, which to a Satnav will also be the shortest route.

Indeed. Sometimes I've programmed a route in Google and been annoyed that it's tried sending me the long way round, others I've surprised that it's sent me the directest route instead. I guess it just depends upon the time of day, and other parameters (e.g. collisions, heavy traffic, obstructions, roadworks).

[jackal]

Interesting figures, thank you. By far the biggest flows are to/from Taunton town, rather than any longer distance ones.

Which is both intuitively what I expected, and also what would be standard in such a situation.

Were it not such a constrained site it would be a good candidate for a stackabout.

[mapboy]

Interesting figures, thank you. By far the biggest flows are to/from Taunton town, rather than any longer distance ones.

Which is both intuitively what I expected, and also what would be standard in such a situation.

Were it not such a constrained site it would be a good candidate for a stackabout.

I am of the opinion that this strengthens the argument for a higher quality interchange between the A358 and M5, such that local Taunton traffic is not mixed needlessly with long-distance strategic traffic.

[Scratchwood]

If they want traffic to go up the A358 then the A303/358 junction needs to prioritise this route instead of the A303. Whether this is done by bypassing the junction and making the desired route the mainline or by cheaper methods like signage or alterations to the existing roundabout will depend on budgets and will to do it. But unless something like this is done, traffic will probably still want to take what appears to be the more direct or shorter route, regardless of the road standard.

Satnavs will also play a role here. They tend to offer either the shortest abd/or fastest route. There will be occasions when the M5 is busy and it might actually be quicker to go A303/A30, which to a Satnav will also be the shortest route.

If lots of people divert up the A358 route, then the old route via Blackdown will be an attractive drive, not much slower, and much more scenic

[multiraider2]

If lots of people divert up the A358 route, then the old route via Blackdown will be an attractive drive, not much slower, and much more scenic

Yes. When the A358 scheme was first proposed some years ago, I stated on this forum that I would likely go the old way. If there is a proper dualled expressway along the whole length of the A303, I would likely return to the A303 for my trips to the SW but, subject to the amount of traffic that remains and including even a renumbering of the A358 and a bypassing of Southfields, still get to and go the old way from Southfields.

It might be even more difficult to change behaviour on the return trip, as drivers will habitually turn off the M5 at Jnc. 29 for the A303 and nothing can deny the fact that Jnc. 25 will always still be many miles ahead.

[Scratchwood]

If lots of people divert up the A358 route, then the old route via Blackdown will be an attractive drive, not much slower, and much more scenic

Yes. When the A358 scheme was first proposed some years ago, I stated on this forum that I would likely go the old way. If there is a proper dualled expressway along the whole length of the A303, I would likely return to the A303 for my trips to the SW but, subject to the amount of traffic that remains and including even a renumbering of the A358 and a bypassing of Southfields, still get to and go the old way from Southfields.

It might be even more difficult to change behaviour on the return trip, as drivers will habitually turn off the M5 at Jnc. 29 for the A303 and nothing can deny the fact that Jnc. 25 will always still be many miles ahead.

Outside the the busiest months, I've generally found Blackdown a very pleasant drive, one where you can still drive at 50/60 for most of its length (other than THAT 90 degree bend!), it's probably only 3 months of the year when it's a serious bottleneck?

[TimM3-A55]

So why is it that the government don't seem to believe it, as that's plainly their/HE's motivation for backing the scheme??

They must believe that the disbenefits of a 9-mile northerly diversion are outweighed by the faster journey times once you hit the motorway. I am not convinced by this - any diversion that takes you on a longer route is counter-productive - unless the original route is inherently unreliable, which I don't believe the Blackdown stretch is. It is not unlike other similar A-roads (admittedly no longer trunk, in many cases).

Some quick and dirty maths shows that assuming an average speed of 70mph on the M5 and upgraded A358 your average speed on the A303/A30 would have to drop below 54mph to be slower than the M5. Given nearly half the route is on the upgraded A30 after Honiton this seems unlikely.

It's just easier (cheaper) to upgrade one route not two, particularly if you pick the shorter and easier route in the first place. The GOV just won't admit it.

Interesting figures, thank you. By far the biggest flows are to/from Taunton town, rather than any longer distance ones.

Which is both intuitively what I expected, and also what would be standard in such a situation.

Were it not such a constrained site it would be a good candidate for a stackabout.

I am of the opinion that this strengthens the argument for a higher quality interchange between the A358 and M5, such that local Taunton traffic is not mixed needlessly with long-distance strategic traffic.

A stackabout would be the best solution, notoriously difficult to do to an existing junction though. There certainly isn't space for a fix like the M4/A34 or M40/A46 junction, To me the best option would be to build a new stackabout junction just a little further north and link the new road to the old with a roundabout by demolishing the MacDonalds. Either fully close the existing junction or just leave the south facing slips open as a local junction. Not essay to do as there's a few rivers and a railway line in the way. I don't think the proposed new road would link in well either, but then it wouldn't in its current form.

Is there details on what the junction with the A303 will be? The last scheme had a dumbbell I think, the thought of that horrified me, and to be fair was probably part of how they would "encourage" people to use the new route. If it had been built as such there's a high chance it would be in CBRD's bad junctions by now, the queues on a summer Saturday would be notorious. Ideally a three-way meeting point between two grade separated D2 routes should be a trumpet, not so easy as the current roundabout links other routes as well. A roundabout interchange, hopefully with free-flowing links to the route that doesn't have priority through the junction, would be easier. jackal you didn't happen to find turning statitics for the A303/A358 junction in the same place you found the ones for the M5 junction did you?

[Sou'wester]

To non locals, no one understands why you'd dual the A358 instead of the A303.

If you're a local, you know why.

Ideally you'd do both, but if only one can be chosen IMO it should always be the A358. It is always busy, unlike the tourist route A303.

Unless it is evening you'd struggle to ever average close to 60mph on the A358.

Edit: AADT Figures for 2016:

A303 - 13,000
A358 - 21,000

No brainer.

[Richardf]

The best thing for the A303/358 junction is for it to be bypassed offline with a GSJed link to the existing roundabout and other routes. I think one of the earlier plans had this, but will probably be watered down now.

[Chris5156]

It's just easier (cheaper) to upgrade one route not two, particularly if you pick the shorter and easier route in the first place. The GOV just won't admit it.

It's certainly easier. The Blackdown Hills are a designated Area of Outstanding Natural Beauty and building a major expressway through them will be a long, hard slog through the planning process. The A303 already has enough long, hard slogs through the planning process with Stonehenge and the cost/benefit of improving the route to expressway is tested enough by the cost of all that. Introducing another section that would likely get swamped by environmental concerns and require lots of expensive mitigation work is not something they'll want to do lightly. So from that point of view the A358 is the pragmatic choice.

I don't like it any more than anyone else, of course, and when I have cause to take the A303 I'll carry on down to Honiton with everyone else. I do wonder whether it'll end up back in the programme at some point in another 10-20 years.

[A303Chris]

It's just easier (cheaper) to upgrade one route not two, particularly if you pick the shorter and easier route in the first place. The GOV just won't admit it.

I don't like it any more than anyone else, of course, and when I have cause to take the A303 I'll carry on down to Honiton with everyone else. I do wonder whether it'll end up back in the programme at some point in another 10-20 years.

As a regular user of both the A303 and M4/M5, if I used the A303 I would still go to Honiton, especially if the rest of the road was dual carriageway.

When I go to Plymouth for a 10.30 meeting if I leave Reading at 7, I get stuck around Bristol in rush hour, however if I use the A303 between 8 and 9 I am somewhere between Andover and Castle Cray. Unless it is a Friday or Saturday during the holiday season, I've have never been held up and usually average 50mph on the single lane sections. On a clear run it takes about 2.5 hours going A303 compared to just over 2 using the M4/M5. However I saved 20 miles and had a much less stressfull journey.

If all the rest is dualed the total length of the single section between Horton and Honiton is 13 miles given the short dual section in the middle. Even if stuck at 40mph through here it will still be quicker then going the extra 15 miles at 70 mph along the A358 and M5.

As the traffic counts show , only 13,000 vehicles on average use the Blackdown Hill section, so apart from 10 weekends in a year (30 days max) the road is free flowing

[Berk]

A Knightshayne bypass would be really appreciated too, even if it was just S2. Like you say, the character of the road is more or less up to the task.

[SouthWest Philip]

I wonder if we could end up with a situation where the existing A303 across the Blackdowns sees an increase in traffic in spite of the A358 being dualled? Could easily see a fully dualled Taunton to Popham route attracting say an extra 10k plus vehicles a day of which half might stick with the old road west of Ilminster.

[jackal]

To non locals, no one understands why you'd dual the A358 instead of the A303.

If you're a local, you know why.

Ideally you'd do both, but if only one can be chosen IMO it should always be the A358. It is always busy, unlike the tourist route A303.

Unless it is evening you'd struggle to ever average close to 60mph on the A358.

Edit: AADT Figures for 2016:

A303 - 13,000
A358 - 21,000

No brainer.

Exactly, the A303 in the Blackdown Hills is a pretty ordinary rural A road with ordinary rural A road speeds 90% of the time, while the A358 is just a horrific congested slog.

Unfortunately many people don't have a clue how busy the roads are. The A303 is the more recognizable number so they think that must be the priority.

[TimM3-A55]

To non locals, no one understands why you'd dual the A358 instead of the A303.

If you're a local, you know why.

Ideally you'd do both, but if only one can be chosen IMO it should always be the A358. It is always busy, unlike the tourist route A303.

Unless it is evening you'd struggle to ever average close to 60mph on the A358.

Edit: AADT Figures for 2016:

A303 - 13,000
A358 - 21,000

No brainer.

I don't think anyone is claiming that the A358 doesn't need an upgrade, the consensus seems to be that it isn't and won't be part of the south West route linking the M3 and M5. Therefore the proposed upgrade is designed for a job the A358 won't do at the expense of what it actually does. None of the upgrades will do much for the overload M5 junction.

I don't like it any more than anyone else, of course, and when I have cause to take the A303 I'll carry on down to Honiton with everyone else. I do wonder whether it'll end up back in the programme at some point in another 10-20 years.

Quite possible, the issue with that is that any lower quality upgrades to the blackdown hills section in the interim, like the S2+1 Devonhouse upgrade, will become bottlenecks if the rest is upgraded to D2. Maybe the HA should stipulate that any Local authority funded upgrades should be to D2 or easily expanded to D2.

[Chris5156]

Quite possible, the issue with that is that any lower quality upgrades to the blackdown hills section in the interim, like the S2+1 Devonhouse upgrade, will become bottlenecks if the rest is upgraded to D2. Maybe the HA should stipulate that any Local authority funded upgrades should be to D2 or easily expanded to D2.

Do we know that the Blackdown Hills section will remain a trunk road once the A358 scheme is done? If it gets detrunked and reverts to Devon CC, then HE will have no say over what happens to it or what standard any work is carried out to.

[wrinkly]

Do we know that the Blackdown Hills section will remain a trunk road once the A358 scheme is done? If it gets detrunked and reverts to Devon CC, then HE will have no say over what happens to it or what standard any work is carried out to.

I'm certainly expecting it to be detrunked. I thought the whole point was that the A303/A30 between Southfields and Honiton will be detrunked and will remain single carriageway.