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Glenn A wrote: ↑Sun Apr 21, 2019 14:46
The Greymoorhill Interchange is one big bad mother. With the A689 Carlisle NDR and increased traffic on the A689 to Linstock, it is a lot more complex and busier than it was ten years ago and near misses and traffic light jumping are common. Also prior to 1970, I didn't realise the A74 forked away from the A7 in Kingstown and went along Parkhouse Rd where the Asda is now.
When I was in Carlisle a few years ago, I glanced through a book of old photographs which showed that the HSBC Bank in this picture (it is now a Subway) was in the middle of a traffic island with Kingstown Road being a no-entry for northbound traffic; all traffic for the A7 had to pass to the left of the HSBC Bank then bear right around the island to rejoin Kingstown Road, while the A74 traffic headed out of the city along Parkhouse Road.
Glenn A wrote: ↑Sun Apr 21, 2019 14:46
The Greymoorhill Interchange is one big bad mother. With the A689 Carlisle NDR and increased traffic on the A689 to Linstock, it is a lot more complex and busier than it was ten years ago and near misses and traffic light jumping are common. Also prior to 1970, I didn't realise the A74 forked away from the A7 in Kingstown and went along Parkhouse Rd where the Asda is now.
When I was in Carlisle a few years ago, I glanced through a book of old photographs which showed that the HSBC Bank in this picture (it is now a Subway) was in the middle of a traffic island with Kingstown Road being a no-entry for northbound traffic; all traffic for the A7 had to pass to the left of the HSBC Bank then bear right around the island to rejoin Kingstown Road, while the A74 traffic headed out of the city along Parkhouse Road.
jackal wrote: ↑Wed Oct 26, 2016 20:09
The M25/A3 has the more conventional arrangement with the stackabout sat in the middle of the three levels. IMO this makes it well suited to replacement with two opposing semi-direct right turns at that level that do not cross, in the classic stack-type arrangement. The other two right turns could be provided with semi-direct ramps above or below the existing levels of the junction (making a four-level stack), as loops (making a cloverstack), as cyclic connectors around the edge of the junction (making a three-level cloverturbine), or as some combination of these.
But you have to remember that, at least until they sort out the missing flows at the Ockham junction, and not forgetting the RHS Wisley LILO, the stackabout is an essential u-turn opportunity (adding to the traffic on the junction)
I think all the U-turn movements are being redirected to the next junctions in each direction:
Why does that design retain a roundabout "for local/pedestrian/horse/etc use"? Surely that traffic CAN'T use the M25 and therefore has no need for provision for turns?
Why does that design retain a roundabout "for local/pedestrian/horse/etc use"? Surely that traffic CAN'T use the M25 and therefore has no need for provision for turns?
For U-turns as the roundabout is (and would be) the only way to access some local A3 junctions.
As noted above, access away from J10 will be provided for this traffic under the proposed scheme. Unfortunately this doesn't seem to have been considered for the freeflow options, hence why they're so overbuilt with massive land take and some five levels in the case of the stack!
Veloel wrote: ↑Mon Apr 22, 2019 13:55Why does that design retain a roundabout "for local/pedestrian/horse/etc use"? Surely that traffic CAN'T use the M25 and therefore has no need for provision for turns?
Road users who can't use the M25 may still want to make U-turns ... this is traffic that is on the A3 and wants to carry on using the A3, it is a complete coincidence that the junction is with a motorway, and it's a bit of a red herring to talk about non-motorway traffic there because I can't imagine many cyclists or horsists using that roundabout! But there are several LILO access points to the A3 between the Ripley and Cobham junctions, and removing the U-turn options would require traffic wanting to use those access points to continue to the next junction, regardless of whether they are allowed on a motorway or not. If you are coming out of RHS Wisley and you want to head towards Guildford then you need to turn left onto the A3 and then turn round.
In any junction like this, the right turns will have different flows. Off the top of my head I would guess the dominant one is from Heathrow to Guildford, M25E to A3S. Taking the largest right turn flow out can liberate the rest.
The other issue is left turners on the roundabout. This traffic is readily removed by provision of freeflow left turn slip lanes, which take very little extra space. For some reason HE have got it in for freeflow left turn slip lanes, even removing some that already exist
I can see why this was rejected as the forest take is indeed huge.
As a regular (until recently) user of this Jn I would say the principal right turn flows are from the A3, A3N to M25E and A3S to M25W.
The left turns apart from A3N-M25W seem lightly used although M25W-A3N would be ideal as a freeflow shortcut.
At the moment the conflicting turns but no space on the roundabout lead to short light intervals hence slow throughout and queuing back onto the A3 mainlines with attendant congestion on the A3 proper. The M25 copes better as the slips are large.
Removal (freeflow) of just one or two conflicting moves would be ideal.
Adding space on the roundabout makes sense as at the moment more than half a dozen cars leads to blocking subsequent light release flows and essentially near gridlock. It doesnt help also the lane changes you seem to need/expected to make and lack of markings/signage.
WHBM wrote: ↑Tue Apr 23, 2019 11:29
In any junction like this, the right turns will have different flows. Off the top of my head I would guess the dominant one is from Heathrow to Guildford, M25E to A3S. Taking the largest right turn flow out can liberate the rest.
The other issue is left turners on the roundabout. This traffic is readily removed by provision of freeflow left turn slip lanes, which take very little extra space. For some reason HE have got it in for freeflow left turn slip lanes, even removing some that already exist
Three of the right turns are busy, with East to North rather less so:
marconaf wrote: ↑Tue Apr 23, 2019 16:14
I can see why this was rejected as the forest take is indeed huge.
jackal wrote: ↑Tue Feb 27, 2018 12:02Looking through some of the rejected options, here's another frustration - an option to provide one freeflow right turn would actually have lower land take than an elongated roundabout with freeflow left turns.
Furthermore, the land take for the proposed scheme is an astonishing 26 hectares! (See here, p. 8.) Even supposing that this accounts for elements excluded from the preliminary drawings above, they could surely have provided one freeflow right turn within such a large land take. So there's not even any real environmental argument for the preferred option.
WHBM wrote: ↑Tue Apr 23, 2019 11:29
The other issue is left turners on the roundabout. This traffic is readily removed by provision of freeflow left turn slip lanes, which take very little extra space. For some reason HE have got it in for freeflow left turn slip lanes, even removing some that already exist
I agree there should be more free flow left turns. I know you have to accommodate the merging of the free flow which may mean a wider slip road. But if lack of capacity on the roundabout is the problem this seems an obvious way to help.
BUMP. It seems I neglected to add A19/A1058 when it opened in early 2019, so I've done so now. This was the first newly qualifying interchange in England since 2004. It will be followed by the under construction M2/A249 and A1/A421.
jackal wrote: ↑Fri Apr 05, 2024 10:13
BUMP. It seems I neglected to add A19/A1058 when it opened in early 2019, so I've done so now. This was the first newly qualifying interchange in England since 2004. It will be followed by the under construction M2/A249 and A1/A421.
Unfortunately depending on your definition there may once again be no net gain, because the northbound tunnel of A38/B4114 has now become a bus lane.
I don't know if this actually withdraws it as the physical uninterrupted route still exists, but it's not open to general traffic.
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jackal wrote: ↑Fri Apr 05, 2024 10:13
BUMP. It seems I neglected to add A19/A1058 when it opened in early 2019, so I've done so now. This was the first newly qualifying interchange in England since 2004. It will be followed by the under construction M2/A249 and A1/A421.
Unfortunately depending on your definition there may once again be no net gain, because the northbound tunnel of A38/B4114 has now become a bus lane.
I don't know if this actually withdraws it as the physical uninterrupted route still exists, but it's not open to general traffic.
Good point. I'll leave it in for now. As you say, it does not obviously fall outside the qualifying conditions.
One of them even made it into the consultation (sort of):
But they preferred to stick with a roundabout.
What I don't understand, is why they didn't consider a similar layout but much smaller, with 30mph limits or whatever, and far less land take. Wouldn't that have been far more sensible than spending £300,000,000 on a bigger roundabout?
Kemplay Bank roundabout is to be replaced when the A66 is upgraded in the next few years. This will see the A66 flyover the current roundabout and avoid the A6 and A686 and end the delays at the traffic lights.
Glenn A wrote: ↑Sat Apr 06, 2024 19:16
Kemplay Bank roundabout is to be replaced when the A66 is upgraded in the next few years. This will see the A66 flyover the current roundabout and avoid the A6 and A686 and end the delays at the traffic lights.
It doesn't meet the criteria of this thread though as the A6 mainline won't be freeflow.
One of them even made it into the consultation (sort of):
But they preferred to stick with a roundabout.
What I don't understand, is why they didn't consider a similar layout but much smaller, with 30mph limits or whatever, and far less land take. Wouldn't that have been far more sensible than spending £300,000,000 on a bigger roundabout?
They seem to have treated retention of the existing rbt as highly desirable, for buildability and local access. So the stack went over the top (5 levels), the cyclic design went around the outside, and the elongated rbt bridges sit next to the existing bridges. This limited the potential for tighter turns other than loops.
Option 9, which was consulted on and was basically a half stack (two of the four freeflow right turns of the stack), was really a very good design that would have left little conflict on the rbt (one of two remaining at-grade movements, westbound to northbound, is minor).
It turned out even option 9 was too ambitious, especially in terms of land (forest) take. It's a real shame they didn't consult on an option with a single freeflow right turn (a quarter stack), which would have been cheaper and better than the long rbt.
Ultimately I don't think an option with tighter turns would really have given much advantage over the half or quarter stack. They did look at options with tight loops (see thread link above - probably the place to continue this discussion).
remember hearing someone describe ' 'Spaguetti Junction' ' in Birmingham as a ' 'stafford knot' '!
What a shame that particular Junction is in Warwickshire :[
varga wrote: ↑Sat Apr 13, 2024 13:43
remember hearing someone describe ' 'Spaguetti Junction' ' in Birmingham as a ' 'stafford knot' '!
What a shame that particular Junction is in Warwickshire :[
Have you heard of a stafford knot in any other context? I haven't.
Edit: I see from Wikipedia it's the traditional symbol of Stafford and Staffordshire. I never knew that before, despite having relatives in Walsall.
varga wrote: ↑Sat Apr 13, 2024 13:43
remember hearing someone describe ' 'Spaguetti Junction' ' in Birmingham as a ' 'stafford knot' '!
What a shame that particular Junction is in Warwickshire :[
Have you heard of a stafford knot in any other context? I haven't.
Edit: I see from Wikipedia it's the traditional symbol of Stafford and Staffordshire. I never knew that before, despite having relatives in Walsall.
that exactly. I think the pretzel they call the 'stafford knot' in Staffordshire is wellknown, though I do not think its recognition is nearly so universal like the 'rose' symbols of Lancaster and York ...
except to Australians that is, the Brisbane coat of arms bears the knot, that particular city is named for someone called Brisbane who served in the Staffordshire regiment is why
