A428 Black Cat - Caxton Gibbet improvement

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KeithW
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Re: Black Cat - Cambourne rumour?

Post by KeithW »

Herned wrote: Tue Mar 16, 2021 18:29
jackal wrote: Tue Mar 16, 2021 10:09 Costs are astonishing - £286.8 million for option C and £316.2 million for option C+. Please let's never again hear about stackabouts being cheap.
I wonder how much is down to having to build it around two existing dual carriageways? It surely wouldn't cost that in the middle of a field, would it?
You wouldnt need it in the middle of a field, one reason why the Black Cat was a problem for decades was there was always the idea that the A1 would be upgraded to A1(M) offline on a route to the west as was proposed in 1993. After 25 years it got to the point that it was obviously not going to happen and they had run out of space for the ritual of making the Black Cat roundabout larger.

Of course that offline upgrade would be 30 miles long and eye wateringly expensive given the price of land in those parts.
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Re: Black Cat - Cambourne rumour?

Post by mikehindsonevans »

ChrisH wrote: Tue Mar 16, 2021 10:36 The assumptions used in the junction design are interesting. They say that RIS2 requires the creation of a freeflowing network, but defines that as the through-routes not the slip roads. It also specifically mentions that because the A1 will dip and require pumping, that any junction option needs to offer "resilience" of getting traffic off and on again: i.e. the stackabout is the only option. Quelle surprise :roll:
Pumping? Hopefully with a better implementation than the A555 swimming pool at Wilmslow?!?
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Re: Black Cat - Cambourne rumour?

Post by Alderpoint »

mikehindsonevans wrote: Tue Mar 16, 2021 22:44 Pumping? Hopefully with a better implementation than the A555 swimming pool at Wilmslow?!?
They've done a good job on the pumping at Toll Bar - not seen any flooding there since is was built and it's a sizeable dip.
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Re: Black Cat - Cambourne rumour?

Post by Bryn666 »

Is a full movements interchange really even needed here? I know completionists have a fetish for all-ways free-flow interchanges but this is supposed to be a strategic corridor and the 3 level roundabout is known to be the worst of all worlds...

Several of the UK's big consultants can only think of roundabouts. Did you see how many were peppered in the Heathrow Terminal 6 plans by HAL Ltd? If in doubt, stick a roundabout in... :roll:
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Re: Black Cat - Cambourne rumour?

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Bryn666 wrote: Wed Mar 17, 2021 10:04 Is a full movements interchange really even needed here? I know completionists have a fetish for all-ways free-flow interchanges but this is supposed to be a strategic corridor and the 3 level roundabout is known to be the worst of all worlds...

The only movement that isn't really needed is the A1 south to A428 East, and vice versa - as it would only be local traffic wanting to do this, which would be adequately catered for by the existing St Neots southern bypass.

Clearly the local accesess don't help, including the old A421 and the boatyard....

I'm also not sure why the junction isn't doing more creative things and reusing this bridge to create a nice folded diamond for the local connections https://www.google.com/maps/@52.18415,- ... 312!8i6656
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Re: Black Cat - Cambourne rumour?

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c2R wrote: Wed Mar 17, 2021 10:28
The only movement that isn't really needed is the A1 south to A428 East, and vice versa - as it would only be local traffic wanting to do this, which would be adequately catered for by the existing St Neots southern bypass.

Clearly the local accesess don't help, including the old A421 and the boatyard....

I'm also not sure why the junction isn't doing more creative things and reusing this bridge to create a nice folded diamond for the local connections https://www.google.com/maps/@52.18415,- ... 312!8i6656
Its little more than a country lane with a minimal amount of traffic, what more is needed ?
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Re: Black Cat - Cambourne rumour?

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KeithW wrote: Wed Mar 17, 2021 10:51
c2R wrote: Wed Mar 17, 2021 10:28
The only movement that isn't really needed is the A1 south to A428 East, and vice versa - as it would only be local traffic wanting to do this, which would be adequately catered for by the existing St Neots southern bypass.

Clearly the local accesess don't help, including the old A421 and the boatyard....

I'm also not sure why the junction isn't doing more creative things and reusing this bridge to create a nice folded diamond for the local connections https://www.google.com/maps/@52.18415,- ... 312!8i6656
Its little more than a country lane with a minimal amount of traffic, what more is needed ?
Plug the old A421 in there with folded diamond sliproads to the west of the bridge. Also connect the access to the boatyard to it, and any other local access that you want away from the main junction, close the black cat filling station, and then build something better than a stackabout to the east.
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Re: Black Cat - Cambourne rumour?

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Bryn666 wrote: Wed Mar 17, 2021 10:04 Is a full movements interchange really even needed here? I know completionists have a fetish for all-ways free-flow interchanges but this is supposed to be a strategic corridor and the 3 level roundabout is known to be the worst of all worlds...

Several of the UK's big consultants can only think of roundabouts. Did you see how many were peppered in the Heathrow Terminal 6 plans by HAL Ltd? If in doubt, stick a roundabout in... :roll:
I've said it from day 1, the stackabout is a bad design for this location. They are okay where you need full access and have moderate turning volumes. Here some movements are not needed at all, while A1 southbound to A421 is very heavy and still will be with the A428 traffic removed:

A428 AADT 2040 - Copy.JPG

You can see that, with the new road, volumes are about 30k AADT higher on A1 north and A421 than on A1 south and A428.

How does traffic get between the two dominant arms of this £300m multi-level interchange? Through the roundabout of course, because that's how things are done in the UK. Another fine pinchpoint in the making, to be fixed a couple of decades down the line for a further £300m+massive construction inflation :facepalm:

https://infrastructure.planninginspecto ... ndix_C.pdf
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Re: Black Cat - Cambourne rumour?

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jackal wrote: Wed Mar 17, 2021 11:13
Bryn666 wrote: Wed Mar 17, 2021 10:04 Is a full movements interchange really even needed here? I know completionists have a fetish for all-ways free-flow interchanges but this is supposed to be a strategic corridor and the 3 level roundabout is known to be the worst of all worlds...

Several of the UK's big consultants can only think of roundabouts. Did you see how many were peppered in the Heathrow Terminal 6 plans by HAL Ltd? If in doubt, stick a roundabout in... :roll:
I've said it from day 1, the stackabout is a bad design for this location. They are okay where you need full access and have moderate turning volumes. Here some movements are not needed at all, while A1 southbound to A421 is very heavy and still will be with the A428 traffic removed:


A428 AADT 2040 - Copy.JPG


You can see that, with the new road, volumes are about 30k AADT higher on A1 north and A421 than on A1 south and A428.

How does traffic get between the two dominant arms of this £300m multi-level interchange? Through the roundabout of course, because that's how things are done in the UK. Another fine pinchpoint in the making, to be fixed a couple of decades down the line for a further £300m+massive construction inflation :facepalm:

https://infrastructure.planninginspecto ... ndix_C.pdf
It can only be because the design requirements for 'free-flow' interchanges are so ridiculous that nobody can design one. That said, they managed it on the A14... just abouts.
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Re: Black Cat - Cambourne rumour?

Post by Herned »

How does a dual carriageway in Cambridgeshire cost £140m a mile. What exactly costs so much money? Even ignoring the ludicrous cost of the Black Cat interchange, it's still north of £100m per mile.
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Re: Black Cat - Cambourne rumour?

Post by KeithW »

c2R wrote: Wed Mar 17, 2021 10:54 Plug the old A421 in there with folded diamond sliproads to the west of the bridge. Also connect the access to the boatyard to it, and any other local access that you want away from the main junction, close the black cat filling station, and then build something better than a stackabout to the east.
This is far too late in the day to make radical changes, access to the boatyard is going be a separate issue.
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Re: Black Cat - Cambourne rumour?

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KeithW wrote: Wed Mar 17, 2021 14:18
c2R wrote: Wed Mar 17, 2021 10:54 Plug the old A421 in there with folded diamond sliproads to the west of the bridge. Also connect the access to the boatyard to it, and any other local access that you want away from the main junction, close the black cat filling station, and then build something better than a stackabout to the east.
This is far too late in the day to make radical changes, access to the boatyard is going be a separate issue.
Yeah, it's why I suggested it at the initial consultation.
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Re: Black Cat - Cambourne rumour?

Post by jackal »

c2R wrote: Wed Mar 17, 2021 10:54 Plug the old A421 in there with folded diamond sliproads to the west of the bridge. Also connect the access to the boatyard to it, and any other local access that you want away from the main junction, close the black cat filling station, and then build something better than a stackabout to the east.
It's difficult to do much with that bridge as it's so close to Black Cat. They're demolishing it in fact.

The boatyard has its own little bridge and access track built with the current scheme.
Herned wrote: Wed Mar 17, 2021 13:30 What exactly costs so much money? Even ignoring the ludicrous cost of the Black Cat interchange, it's still north of £100m per mile.
Viaduct over the River Great Ouse, bridge over the ECML, two dumbells, dozens of other structures, major earthworks along most of the route.

There are similar prices on the A12, A14, and A120 schemes. It's just what a well engineered road in this part of the world costs nowadays.

Detailed plan: https://highwaysengland.citizenspace.co ... 0Plans.pdf
Last edited by jackal on Wed Mar 17, 2021 16:09, edited 1 time in total.
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Re: Black Cat - Cambourne rumour?

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jackal wrote: Wed Mar 17, 2021 15:57 There are similar prices on the A12, A14, and A120 schemes. It's just what a well engineered road in this part of the world costs nowadays.
The A421 Bedford to M1 cost £154m (£19.5m per mile), in very similar terrain including three junctions and a bridge over the M1.

That opened in 2010, I know construction inflation runs ahead of RPI but that is five times as much per mile.

Where does that money go?
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Re: Black Cat - Cambourne rumour?

Post by JammyDodge »

Herned wrote: Wed Mar 17, 2021 16:04
jackal wrote: Wed Mar 17, 2021 15:57 There are similar prices on the A12, A14, and A120 schemes. It's just what a well engineered road in this part of the world costs nowadays.
The A421 Bedford to M1 cost £154m (£19.5m per mile), in very similar terrain including three junctions and a bridge over the M1.

That opened in 2010, I know construction inflation runs ahead of RPI but that is five times as much per mile.

Where does that money go?
Looking at the General Arrangement Plans, I think you underestimated the amount of earthworks in this scheme when compared to the A421 Bedford - M1. There is also the matter of a new GSJ for the A1 and A421, which also build a significant amount of new local roads, as well as land costing more in this area of the country.
You also have a significant number of bridges, for the A421, new junctions and access roads
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Re: Black Cat - Cambourne rumour?

Post by trickstat »

JammyDodge wrote: Wed Mar 17, 2021 17:23
Herned wrote: Wed Mar 17, 2021 16:04
jackal wrote: Wed Mar 17, 2021 15:57 There are similar prices on the A12, A14, and A120 schemes. It's just what a well engineered road in this part of the world costs nowadays.
The A421 Bedford to M1 cost £154m (£19.5m per mile), in very similar terrain including three junctions and a bridge over the M1.

That opened in 2010, I know construction inflation runs ahead of RPI but that is five times as much per mile.

Where does that money go?
Looking at the General Arrangement Plans, I think you underestimated the amount of earthworks in this scheme when compared to the A421 Bedford - M1. There is also the matter of a new GSJ for the A1 and A421, which also build a significant amount of new local roads, as well as land costing more in this area of the country.
You also have a significant number of bridges, for the A421, new junctions and access roads
Including a bridge over the East Coast Main Line.
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Re: Black Cat - Cambourne rumour?

Post by Herned »

JammyDodge wrote: Wed Mar 17, 2021 17:23
Looking at the General Arrangement Plans, I think you underestimated the amount of earthworks in this scheme when compared to the A421 Bedford - M1. There is also the matter of a new GSJ for the A1 and A421, which also build a significant amount of new local roads, as well as land costing more in this area of the country.
You also have a significant number of bridges, for the A421, new junctions and access roads
Land costs are practically a rounding error - £1m per km would be 3-4 times the going rate for the best farmland in the country

The A6 in Northern Ireland goes through actual uplands with serious earth-moving, and is costing nothing like £60m per km (the cost excluding the Black Cat interchange). The Clydach Gorge section of the A465 is costing less per km.

This scheme has 6 overbridges and 4 underbridges, as well as the two interchanges. Nothing out of the ordinary

I just don't see why costs have gone up so dramatically in ten years
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Re: Black Cat - Cambourne rumour?

Post by Bryn666 »

Herned wrote: Wed Mar 17, 2021 21:21
JammyDodge wrote: Wed Mar 17, 2021 17:23
Looking at the General Arrangement Plans, I think you underestimated the amount of earthworks in this scheme when compared to the A421 Bedford - M1. There is also the matter of a new GSJ for the A1 and A421, which also build a significant amount of new local roads, as well as land costing more in this area of the country.
You also have a significant number of bridges, for the A421, new junctions and access roads
Land costs are practically a rounding error - £1m per km would be 3-4 times the going rate for the best farmland in the country

The A6 in Northern Ireland goes through actual uplands with serious earth-moving, and is costing nothing like £60m per km (the cost excluding the Black Cat interchange). The Clydach Gorge section of the A465 is costing less per km.

This scheme has 6 overbridges and 4 underbridges, as well as the two interchanges. Nothing out of the ordinary

I just don't see why costs have gone up so dramatically in ten years
Design consultants aren't cheap either :roll:
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Re: Black Cat - Cambourne rumour?

Post by jackal »

Herned wrote: Wed Mar 17, 2021 21:21
JammyDodge wrote: Wed Mar 17, 2021 17:23
Looking at the General Arrangement Plans, I think you underestimated the amount of earthworks in this scheme when compared to the A421 Bedford - M1. There is also the matter of a new GSJ for the A1 and A421, which also build a significant amount of new local roads, as well as land costing more in this area of the country.
You also have a significant number of bridges, for the A421, new junctions and access roads
Land costs are practically a rounding error - £1m per km would be 3-4 times the going rate for the best farmland in the country

The A6 in Northern Ireland goes through actual uplands with serious earth-moving, and is costing nothing like £60m per km (the cost excluding the Black Cat interchange). The Clydach Gorge section of the A465 is costing less per km.
You have to make sure you're comparing like with like though. For instance the A428 was priced at £707m just three years ago. I'm not sure what is included in the maximal figure of £1.4bn now quoted but it could well largely be down to interest etc. Likewise A465 sections 5 and 6 is £550m construction, £1.14m including financing. Frankly it's hopeless comparing across highways authorities due to such differences.
This scheme has 6 overbridges and 4 underbridges, as well as the two interchanges. Nothing out of the ordinary
Try doubling that.
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Re: Black Cat - Cambourne rumour?

Post by Herned »

jackal wrote: Thu Mar 18, 2021 00:21 Try doubling that.
That is from the map, and ignoring the Black Cat interchange. I may have miscounted, but even so it's still nothing put of the ordinary for a route in open countryside.

The costs, excluding the interchange, are much higher than other schemes elsewhere in the UK. I take your point that the costs aren't directly comparable, but there can't be much variation in the cost of building a single overbridge, or moving 1 m3 of earth. Labour costs will be different, but no more than 20% or so.

There must be some explanation
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