The study of British and Irish roads - their construction, numbering, history, mapping, past and future official roads proposals and general roads musings.
There is a separate forum for Street Furniture (traffic lights, street lights, road signs etc).
Registered users get access to other forums including discussions about other forms of transport, driving, fantasy roads and wishlists, and roads quizzes.
Bryn666 wrote:In terms of 'neatness' it's Purple route and option C for me.
C is just a stacked roundabout. We've seen time and time again that these aren't suited to high turning volumes. Do we really have to keep repeating the same mistake?
A is a Pareto optimal improvement (as the economists say) on C in terms of freeflow - A freeflows both mainlines, like C, but adds the A1sb->A421 freeflow.
Better a messy interchange with freeflow out the wazoo than a nice neat stackabout that clogs up soon after opening.
Bryn666 wrote:In terms of 'neatness' it's Purple route and option C for me.
C is just a stacked roundabout. We've seen time and time again that these aren't suited to high turning volumes. Do we really have to keep repeating the same mistake?
A is a Pareto optimal improvement (as the economists say) on C in terms of freeflow - A freeflows both mainlines, like C, but adds the A1sb->A421 freeflow.
Better a messy interchange with freeflow out the wazoo than a nice neat stackabout that clogs up soon after opening.
I'd go for Purple - A as well. More off line construction than C so should be less of a nightmare for drivers during construction as well.
Option C with the same freeflow movements as A, plus two left turn bypasses of the main roundabout. There are only 4 structures over the existing A1 with my suggestion, as opposed to 5 with Option A. With my spare bridge I have turned the old northbound carriageway into a local access road between the old Bedford Road and the existing southbound offslip for Tempsford. This provides a new GSJ to take the marina off the A1 mainline.
Additionally, if it is required, a TRSA could be provided to replace the existing service area that will need demolishing for any of the options to be built (except B, but that's the rubbish option).
So, removed local accesses onto the mainline, and a less complicated knot of sliproads to build or navigate once open. I'll accept my fee in jaffa cakes, thank you
Bryn Terminally cynical, unimpressed, and nearly Middle Age already. She said life was like a motorway; dull, grey, and long.
Well having just moved away from the area I can now say I no longer have a horse in this race but I would strongly advise the Orange route. Both Purple and Pink take you into or close to areas of Special Scientific Interest and close to largish villages such as Abbotsley which currently attract little through traffic.
The Purple route north of Abbotsley is going to take you through or very close to the golf course and hotel grounds which is based round a mediaeval manorial complex and I guarantee will create all sorts of ructions.
The Pink Route south of Abbotsley will skirt Waresley Park and takes you along the edge of the Greensand Ridge which will complicate the road building process and also attract a lot of protest , this time more from twitchers and hikers rather than golfers
The Orange route on the other hand largely follows the existing traffic corridors crossing open farmland and provides easy road access for the construction process. There will be much less local protest against this route and it will move traffic away from Eltisley and Croxton Park which will make them very happy. I doubt costs would be significantly higher.
As someone who needs this to improve my east-west journeys, rather than being directly affected by the works and so on as a resident, I'd be happy for them to build any of the three options as long as they get on with it.
I seems odd that the orange option should run so close to the existing route but directly incorporate so little of it.
As for the arrangements at Black Cat, the best answer depends on what happens to the A1, in particular whether any future upgrade of the A1 is on-line or off-line. Option B which has the A428 free-flowing and the A1 hitting the existing roundabout at grade should be a runner only if the A1 is going to be upgraded off-line, IMHO.
Turning to the A421/A1 interchange I tend to agree that Option A is probably the way to go. Option C will simply be the 3rd (or is it 4th) enlargement of the Black Cat albeit now lifted above the A1 and Option B is just ludicrous.
I'd vote for the orange option as it uses an existing road corridor and provides better access for St Neots, which would reduce traffic from the existing A428, making it a nicer route for non motorised traffic. Otherwise, there will still be a considerable amount of local commuter traffic using the route. Though that could be considered a good thing I suppose.
I prefer option A for the Black Cat, but this seems strange not to consider alongside the A1 study. If that recommends its option A, for a new motorway along the lines of the 1994 proposals, a large new freeflow junction would need to be constructed to the west of the site here.
Option A is fine, but ideally you'd take Bedford Road away from Black Cat and make it a full freeflow interchange, like this:
Note that this has less structural content than most of the consultation options, with only two levels and three new bridges.
I've put in four slips for Bedford Rd access. There are still a couple of movements to it missing, which could be provided via a smaller GSJ at the marina (which probably has to happen eventually anyway), with access along School Lane.
Last edited by jackal on Mon Mar 06, 2017 19:19, edited 1 time in total.
roadtester wrote:As someone who needs this to improve my east-west journeys, rather than being directly affected by the works and so on as a resident, I'd be happy for them to build any of the three options as long as they get on with it.
I seems odd that the orange option should run so close to the existing route but directly incorporate so little of it.
As for the arrangements at Black Cat, the best answer depends on what happens to the A1, in particular whether any future upgrade of the A1 is on-line or off-line. Option B which has the A428 free-flowing and the A1 hitting the existing roundabout at grade should be a runner only if the A1 is going to be upgraded off-line, IMHO.
As a long term user (at least twice a week for 20 years) of the old A428 there are very good reasons for not using the old road.
In order of issues
1) It is a terrible road with lots of sharp bends, blind corners and at grade junctions with the B1040 at Eltisely being especially problematic with really nasty right hand turns across the carriageway. The accident record for that road is very bad since collisions are frequently high speed impacts. When a car gets t-boned by an HGV doing 50 mph the results are not pretty,
2) The existing route is constrained to the south by conservation areas at Eltisley and Croxton Park so the only way to straighten the road is to build the new route to the North
3) The existing route will see minimal disruption during the new build process
4) The old route can form the basis of the post construction Local Access Road as was done between Hardwicke and Caxton Gibbet when that was dualled
The part that most concerns me about this document is the handwaving associated with the junction at Caxton Gibbet. While it says that it will be improved this is very airy fairy. Caxton Gibbet is already a major bottleneck at busy periods. If traffic flows along the A428 are going to increase it really needs to be freeflow. At a minimum either flyover for the A428 or a stackabout for the A1198. A1198 traffic will only increase given the continued expansion of new housing on the old hospital site in Papworth Everard and at Godmanchester. 30 years ago Papworth was a small village with a large convalescent hospital but it is now becoming a thriving small town it its own right.
KeithW wrote:The part that most concerns me about this document is the handwaving associated with the junction at Caxton Gibbet. While it says that it will be improved this is very airy fairy. Caxton Gibbet is already a major bottleneck at busy periods. If traffic flows along the A428 are going to increase it really needs to be freeflow. At a minimum either flyover for the A428 or a stackabout for the A1198. A1198 traffic will only increase given the continued expansion of new housing on the old hospital site in Papworth Everard and at Godmanchester. 30 years ago Papworth was a small village with a large convalescent hospital but it is now becoming a thriving small town it its own right.
Yes, agreed, Caxton Gibbet really needs fixing and can't be left as is. It would be ridiculous not to fix this leaving it as the only at-grade roundabout between the East Coast and the M1 on the A14/A428/A421 corridor.
That said, Papworth Everard has already had some relief in the form of the fairly new A1198 by-pass.
Are there still plans to realign the A1 in the area? Or is it going to continue going through Black Cat in the forseeable future.
Option A is clearly the best if we're going to retain the A1 going underneath it. However, if there are plans to move the A1 anyway, something less complex and expensive might well make more sense.
Incidentally, Option C is more believable than a stackabout normally is, here; I'm not sure that the turning volumes actually will be all that high once the new route of the A428 is finished. You'd imagine most traffic would be going straight on through the junction. Of course, Option C would be miserable until the A428 upgrade, whereas Option A would work pretty well. (I got the impression from the consultation brochure that the plan was to build the junction first, and the new A428 somewhat later.)
ais523 wrote:Are there still plans to realign the A1 in the area? Or is it going to continue going through Black Cat in the forseeable future.
Option A is clearly the best if we're going to retain the A1 going underneath it. However, if there are plans to move the A1 anyway, something less complex and expensive might well make more sense.
Incidentally, Option C is more believable than a stackabout normally is, here; I'm not sure that the turning volumes actually will be all that high once the new route of the A428 is finished. You'd imagine most traffic would be going straight on through the junction. Of course, Option C would be miserable until the A428 upgrade, whereas Option A would work pretty well. (I got the impression from the consultation brochure that the plan was to build the junction first, and the new A428 somewhat later.)
If you look at the traffic flows along the existing A1/A428 junction you will find a significant amount of traffic heading both north and south up the A1. Southbound obviously includes A421 traffic but there is a lot that is heading for west London and the M25 via the North Orbital. That said Option C is clearly better than Option B but then just about anything would be better than the present setup. Given that there is no sign of the A1(M) upgrade it would be there for at least a decade so lets do it right this time. Once the A428 is upgraded I would expect sigificant increases in traffic volume.
ais523 wrote:Are there still plans to realign the A1 in the area? Or is it going to continue going through Black Cat in the forseeable future.
Option A is clearly the best if we're going to retain the A1 going underneath it. However, if there are plans to move the A1 anyway, something less complex and expensive might well make more sense.
Colour me cynical but this has been the excuse trotted out for not fixing the Black Cat for the last 25 years, enough already.
ais523 wrote:Are there still plans to realign the A1 in the area? Or is it going to continue going through Black Cat in the forseeable future.
Option A is clearly the best if we're going to retain the A1 going underneath it. However, if there are plans to move the A1 anyway, something less complex and expensive might well make more sense.
Colour me cynical but this has been the excuse trotted out for not fixing the Black Cat for the last 25 years, enough already.
I agree to some extent, but if this is built to open in five years time and construction on the 1994 route of the A1(M) opens in (say) ten I'd rather see the money spent on giant freeflow links somewhere else... but on the other hand, the A1 improvements are more like another 30 years away or they opt for further junction improvements along the existing (and very much substandard) route then as you say it needs building 25 years ago!
I can't work out option B: it looks like it is missing various movements, e.g. I don't see any onslip shown for the A428 eastbound. I must be misunderstanding the plan somehow, can anyone work out what's going on?
dcrc2 wrote:I can't work out option B: it looks like it is missing various movements, e.g. I don't see any onslip shown for the A428 eastbound. I must be misunderstanding the plan somehow, can anyone work out what's going on?
My reading of it is that it would be full access via the roundabout on the A1
dcrc2 wrote:I can't work out option B: it looks like it is missing various movements, e.g. I don't see any onslip shown for the A428 eastbound. I must be misunderstanding the plan somehow, can anyone work out what's going on?
My reading of it is that it would be full access via the roundabout on the A1
But then how does it cross the traffic using the A1->A421 loop?
dcrc2 wrote:I can't work out option B: it looks like it is missing various movements, e.g. I don't see any onslip shown for the A428 eastbound. I must be misunderstanding the plan somehow, can anyone work out what's going on?
My reading of it is that it would be full access via the roundabout on the A1
But then how does it cross the traffic using the A1->A421 loop?
That's a very good point. I had assumed (perhaps incorrectly) that it would be strange to cater for A428W->A1S but not the reverse! The same looks true for A428E ->A1S but again not the reverse.
The notes that accompany the pictures state "No change" for these reverse movements - so for A1N-->A421W that implies traffic will use the roundabout and join the A421 towards Bedford; but no change to A1N-->A428E might imply that it will go up to St Neots and across?
I tend to agree that while overall the proposals are impressive the junction improvement maps are not up to HE's usual standards and the absence of any detail concerning the Caxton Gibbet junction is odd.
I can't make head or tail of the Black Cat option B diagram and options A and C appear to have the oddity of right side diverging slips from the A421 eastbound to A1 northbound slip to the roundabout. Black Cat option 3 doesn't seem to have free flow from A1sb to A421wb. So I think on balance from a cursory understanding Black Cat A gets my vote.
Regarding the various routes, I initially assumed that a cross country route would be significantly shorter, but this seems to be not the case, as both of those options are quite circuitous around Abbotsley and Eltisley. Given that the orange route (along the existing route corridor) is barely any longer, is less environmentally sensitive and provides more relief for St.Neots and the existing route, I'm coming round to the orange route.
I think the extent of planned new developments in the area is much bigger than maybe a lot of people might be aware. The consultation document says (Page 11) "Over 50,000 new houses are planned in the immediate area of the A428, A1 and A14, based on a 6.2 mile (10 kilometres) radius. The scheme takes into account the local growth plans, such as St Neots eastern expansion, West Cambourne and Alconbury Weald". That's a lot of extra traffic. Plus with the evidence of substantial rat running in the area (Page 10) already and with the route being part of the Oxbridge Expressway this does seem to be strong justification for the scheme.
owen b wrote:I tend to agree that while overall the proposals are impressive the junction improvement maps are not up to HE's usual standards and the absence of any detail concerning the Caxton Gibbet junction is odd.
I can't make head or tail of the Black Cat option B diagram and options A and C appear to have the oddity of right side diverging slips from the A421 eastbound to A1 northbound slip to the roundabout.
I agree B is a bit of a mess. With A and C, I guess you are talking about the fact that the filter lane bypassing the roundabout is to the left, while the link to the roundabout is to the right? This is a standard arrangement used at dozens of sites across the UK.
Regarding Caxton Gibbet, it should be remembered that this is only a stage 1 consultation, so for an offline scheme like this its perfectly normal to have nothing more than a blob on a map marking the junction location. It will almost certainly be a dumbbell or roundabout interchange.
ais523 wrote:Are there still plans to realign the A1 in the area? Or is it going to continue going through Black Cat in the forseeable future.
The Autumn Statement indicated that the A1 East of England scheme is more of a long term ambition, like the Trans-Pennine Tunnel, than a committed scheme: 'as part of the second Roads Investment Strategy (2020 to 2025), the A66 will be dualled, the Oxford to Cambridge Expressway will be delivered, and improvements will be made to the M60 North West quadrant. In addition, the government will continue to examine the case for improvements to the A1 in the East of England, and for improving connectivity between Sheffield and Manchester'.
Last edited by jackal on Mon Mar 06, 2017 23:52, edited 1 time in total.
