The A30 in Cornwall

[Richardf]

Re the B3285, are you not basing this on the current situation, where traffic for the B3285 has to share one S2 with the A30? Surely once the new A30 is built the traffic will be split, with the B3285 traffic leaving the A30 at Carland and using the old A30 (which then becomes an extension of the B3285). Surely HE have taken this into account and dont see a problem with this situation?

It does though reiterate my previous point about the design at Carland Cross, does it have the capacity for all the required movements if you include A30-B3285 as well as A30-A39? if it does then fine, it avoids an extra junction on the route, if not then maybe you have a case.

At the other end of the scheme, i cant see what benefit a separate, limited junction for the a3075 would be. It would be very close to the north facing slips of the A390 junction at Chiverton x (even if built where the roundabout is now) so would create weaving issues at busy times. I still agree with the HE view, one junction is best.

[jackal]

I think the HE have missed a trick or two with their plans for the dualling of this section of the A30. The first is the obvious one at Chiverton Cross. What I would do is create the interchange junction virtually where the existing Chiverton Cross roundabout is currently, with two roundabouts either side. I would also add a free-flow link from the A390 to A30(W). As for the A3075 (Newquay), I would look at having a new interchange junction just after Chiverton Cross, but with west facing slip roads only (as predominantly, traffic would be flowing from Truro and Redruth to Newquay rather than coming down the A30 and going back on yourself. A30 Chiverton Cross.png

If you look at the public consultation report they respond to this sort of suggestion, pointing out (iirc) that it would be visually intrusive for the nearby church, far more expensive due to the necessity of retaining structures, and massively disruptive for the Cornish economy during construction.

My main issue with the Chiverton Cross design is the severance between the A390 and B3277, for both vehicles and NMUs. This could be resolved with an S2 between them over/under the A30. I think that would be a better use of a second bridge than the two-bridge roundabout, as it would've taken some traffic off the dumbbell while dealing with the severance issue.

[crowntown100]

I think the HE have missed a trick or two with their plans for the dualling of this section of the A30. The first is the obvious one at Chiverton Cross. What I would do is create the interchange junction virtually where the existing Chiverton Cross roundabout is currently, with two roundabouts either side. I would also add a free-flow link from the A390 to A30(W). As for the A3075 (Newquay), I would look at having a new interchange junction just after Chiverton Cross, but with west facing slip roads only (as predominantly, traffic would be flowing from Truro and Redruth to Newquay rather than coming down the A30 and going back on yourself. A30 Chiverton Cross.png

Those slips for the A3075 are far too close the the east facing slips at Chivvy, hence why HE are sharing a junction between the A3075 and A390 (and B3277 and the old road, for that matter).

As for your concerns about the B3285, the road will be extended along the old A30 to meet the new road at Carland Cross, so there isn't that much of an issue there.

I think the design picked for Carland Cross is like that as immediately east of the junction is a very big slope down into the valley. The junction itself pretty much sits in a cutting at the top of a hill, so I think they are trying to minimise the amount of earth that they need to move to build the junction.

My main issue with the Chiverton Cross design is the severance between the A390 and B3277, for both vehicles and NMUs. This could be resolved with an S2 between them over/under the A30. I think that would be a better use of a second bridge than the two-bridge roundabout, as it would've taken some traffic off the dumbbell while dealing with the severance issue.

I think with that you would end up with similar issues with the church, as to add another structure will mean either sinking the A30 into the ground (with associated structures, or lowering the surrounding roads. There just isn't the room to do it. There isn't that much of an issue for vehicles, as they just have to go through the junction, and NMU's are more likely to avoid the area anyway as it's nowhere near anything much. If there is an issue for NMU's, they could always install a footbridge (which shouldn't be too much trouble as the stubs of the old road are still there so there is land to build it).

[Hdeng16]

I realise 2 junctions would be problematic with the close slip roads, but the junction just seems massively underpowered for the various flows. I'm sure there is a lot of through traffic but my experience suggests a lot of different flows which will cross each other.

[jackal]

I think the HE have missed a trick or two with their plans for the dualling of this section of the A30. The first is the obvious one at Chiverton Cross. What I would do is create the interchange junction virtually where the existing Chiverton Cross roundabout is currently, with two roundabouts either side. I would also add a free-flow link from the A390 to A30(W). As for the A3075 (Newquay), I would look at having a new interchange junction just after Chiverton Cross, but with west facing slip roads only (as predominantly, traffic would be flowing from Truro and Redruth to Newquay rather than coming down the A30 and going back on yourself. A30 Chiverton Cross.png

Those slips for the A3075 are far too close the the east facing slips at Chivvy, hence why HE are sharing a junction between the A3075 and A390 (and B3277 and the old road, for that matter).

As for your concerns about the B3285, the road will be extended along the old A30 to meet the new road at Carland Cross, so there isn't that much of an issue there.

I think the design picked for Carland Cross is like that as immediately east of the junction is a very big slope down into the valley. The junction itself pretty much sits in a cutting at the top of a hill, so I think they are trying to minimise the amount of earth that they need to move to build the junction.

My main issue with the Chiverton Cross design is the severance between the A390 and B3277, for both vehicles and NMUs. This could be resolved with an S2 between them over/under the A30. I think that would be a better use of a second bridge than the two-bridge roundabout, as it would've taken some traffic off the dumbbell while dealing with the severance issue.

I think with that you would end up with similar issues with the church, as to add another structure will mean either sinking the A30 into the ground (with associated structures, or lowering the surrounding roads. There just isn't the room to do it. There isn't that much of an issue for vehicles, as they just have to go through the junction, and NMU's are more likely to avoid the area anyway as it's nowhere near anything much. If there is an issue for NMU's, they could always install a footbridge (which shouldn't be too much trouble as the stubs of the old road are still there so there is land to build it).

The route through the junction is 1.2km longer than the status quo. That's what is meant by severance. It may not seem like there's much around here but some people will have their walk to the nearest shops extended significantly.

As for the church, a simple S2 bridge is obviously much less intrusive than a large grade separated junction with slip roads and either a much wider bridge and two roundabouts or two bridges and a large rbt. The slips and rbts also limit bridge placement to where it/they fit rather than where is least intrusive.

Regarding an nmu bridge, that's something they're looking at.

[crowntown100]

The route through the junction is 1.2km longer than the status quo. That's what is meant by severance. It may not seem like there's much around here but some people will have their walk to the nearest shops extended significantly.

As for the church, a simple S2 bridge is obviously much less intrusive than a large grade separated junction with slip roads and either a much wider bridge and two roundabouts or two bridges and a large rbt. The slips and rbts also limit bridge placement to where it/they fit rather than where is least intrusive.

Regarding an nmu bridge, that's something they're looking at.

The only simple solution is an NMU bridge. Any S2 bridge in the area of the current junction is going to be intrusive, no matter what you do with it, as there isn't the room for it without severe disruption. There will also be issues of people using any potential S2 bridge as a rat run to avoid the main junction if it is busy (like the now unclassified road between the A391 and A389, which was used to avoid the old Innis Downs Roundabout), so any idea of an S2 bridge on the current site is dead in the water.

[jackal]

How is it a rat run if it's a purpose built bypass of the main junction?

[A320Driver]

It's pleasing that HE have taken some of the consultation feedback on board, and removed the awful dumbbell. But I still think you will get rat-running from A390 -> A30W.
I really don't buy into the 'construction disruption' argument at Chiverton. The A30 to the west descends into a valley, surely it could flow beneath ground level at a two-bridge roundabout?

One way to construct it would be by building a temporary roundabout just east of Chiverton, linking in the A3075 and taking B3277 and Blackwater traffic with it. This would leave the contractor with the space to excavate/build one of the new bridges at Chiverton, using this to take A390 traffic across the A30 to the A3075.

I can't believe that conversion of a roundabout into a GSJ hasn't been successfully undertaken elsewhere on the network?

[Richardf]

Of course it has. I've seen underpasses and flyovers being built at existing roundabouts. Most of us have here I am sure.

[jackal]

It's possible, just very expensive and disruptive. An example would be Tollbar End, seemingly quite straightforward with just 1 mile of widening and a basic GSJ, but priced over £100m due to the retaining structures and complex traffic management. That would be about half the cost of the entire A30 scheme - not sensible at all when you can build the junction up the road for a fraction of the price.

[SteveA30]

Innis Downs, Bodmin was done, although that was futureproofed anyway. Whiddon Down wasn't partly GS'd but, was converted successfully. The temp rbt at Sourton Down was also converted without problem.

[A320Driver]

I suppose a good example of building a new GSJ off-site would be the new A46 where it meets the A52 at Saxondale.

Back at Chiverton, another option could, in light of moving the GSJ closer to the existing junction, be to build a S2 underbridge at the current junction, just to take the A390-A30(W) flow but appreciate this would add to the cost.
Or even just put a freeflow WB link in.

[Hdeng16]

I hadn't realised they've swapped the dumbells out for a proper roundabout. Did HA say anything about why?

[crowntown100]

How is it a rat run if it's a purpose built bypass of the main junction?

I'm not sure we're on the same wavelength here. However, there still isn't the room to build an S2 bridge there without demolishing the shops and houses that will be severed. However, it would remove the issues of severance, as there would be nothing much left to be severed.

Back at Chiverton, another option could, in light of moving the GSJ closer to the existing junction, be to build a S2 underbridge at the current junction, just to take the A390-A30(W) flow but appreciate this would add to the cost.
Or even just put a freeflow WB link in.

Same as above. Good idea, but not enough room.

I hadn't realised they've swapped the dumbells out for a proper roundabout. Did HA say anything about why?

Locals concerned about capacity of the dumbbell.

[multiraider2]

Here's my route along and avoiding the A30 in Cornwall this year. It only adds 6 miles to the, hopefully obvious to everyone else, route. If you're reading this and thinking of following me, don't. I'm a person of little brain who doesn't know what he is doing. But if Kier haven't finished Temple, at least to four lanes open, then surely only God can help us.

[jackal]

How is it a rat run if it's a purpose built bypass of the main junction?

I'm not sure we're on the same wavelength here. However, there still isn't the room to build an S2 bridge there without demolishing the shops and houses that will be severed. However, it would remove the issues of severance, as there would be nothing much left to be severed.

What a bizarre comment. The natural place for the bridge would be where the existing roundabout is. If there is any additional land take beyond that (which there might not be for a simple S2 bridge with no slips etc) it can easily be accommodated in the fields to the east.

[crowntown100]

How is it a rat run if it's a purpose built bypass of the main junction?

I'm not sure we're on the same wavelength here. However, there still isn't the room to build an S2 bridge there without demolishing the shops and houses that will be severed. However, it would remove the issues of severance, as there would be nothing much left to be severed.

What a bizarre comment. The natural place for the bridge would be where the existing roundabout is. If there is any additional land take beyond that (which there might not be for a simple S2 bridge with no slips etc) it can easily be accommodated in the fields to the east.

But you would have to lower the A30 into cutting on its current alignment to give the clearance for the bridge (as the bridge can't be too high on it'll be intrusive on the church). As there are shops and houses either side, you have issues with subsidence, retaining walls and land acquisition, you'd add a lot to the cost of the scheme just to put the bridge in there for the few people that would use it. I think the current solution is a good compromise for the situation, although the addition of a footbridge/subway at the current junction would be beneficial. Catering for vehicular traffic at a separate bridge on the current site that can easily drive around the junction seems daft to me.

[BF2142]

IIRC, the current Chiv X roundabout is on the top of a hill and has a service area to the north west. I can't see how you could convert the existing junction to some type of higher capacity GSJ without extensive earthworks. I'd be confident it's quicker and cheaper to just move this junction east to where there is space.

[RichardA35]

How is it a rat run if it's a purpose built bypass of the main junction?

I'm not sure we're on the same wavelength here. However, there still isn't the room to build an S2 bridge there without demolishing the shops and houses that will be severed. However, it would remove the issues of severance, as there would be nothing much left to be severed.

What a bizarre comment. The natural place for the bridge would be where the existing roundabout is. If there is any additional land take beyond that (which there might not be for a simple S2 bridge with no slips etc) it can easily be accommodated in the fields to the east.

..and looking at the alignment there is already a 2m deep cutting proposed at the existing roundabout at ch 750, so nearly half the job is already done

[crowntown100]

I'm not sure we're on the same wavelength here. However, there still isn't the room to build an S2 bridge there without demolishing the shops and houses that will be severed. However, it would remove the issues of severance, as there would be nothing much left to be severed.

What a bizarre comment. The natural place for the bridge would be where the existing roundabout is. If there is any additional land take beyond that (which there might not be for a simple S2 bridge with no slips etc) it can easily be accommodated in the fields to the east.

..and looking at the alignment there is already a 2m deep cutting proposed at the existing roundabout at ch 750, so nearly half the job is already done

Fair enough. I get the argument, but still don't see the point in an extra bridge. To me is seems like a lot more money for very little benefit.