N8/N25/N40 - Dunkettle Interchange [open to traffic]

Chris_5339762 · 15-09-2022 9:16pm

The dumbbell once its open, along with the Little Island to Glounthaune link sorts all of this out.

I think it'll go like this -

1) N8E to Glounthaune

2) Little island to Glounthaune link over the new bridge

3) Tunnel realignment. Traffic will go under the new bridge and the roundabout will be extended southwards slightly, allowing the embankments (N25E to M8N) of the new bridge almost to the roundabout to be built.

cargo · 15-09-2022 10:03pm

Ok who's getting the MS Paint out to mark up the expected openings / closures?

AugustusMinimus · 16-09-2022 7:31pm

Most of the ongoing resurfacing work is obviously to realign the tunnel exit to swing further to the east.

However, the gradient and camber of the surface is also being change to allow a smooth swing to the east when exiting. This means that with the current alignment, the surface feels uneven and a bit of a rollercoaster. Obviously this will resolve when the new alignment is in place.

Mushy · 17-09-2022 7:58am

I was surprised that there was reference to opening the new alignment of n25w into the tunnel when from appearance it looks like m8s to n25e would be ready sooner, but don't recall any mention of that opening in any of the emails. Will be a very different place by Christmas, fair play to them

AugustusMinimus · 17-09-2022 10:31am

https://www.boards.ie/discussion/comment/119629570#Comment_119629570

Would prob make the most sense followed by N8S to Tunnel. Tunnel to N8N will take work to the central median exiting the tunnel.

Mushy · 17-09-2022 9:21pm

https://www.boards.ie/discussion/comment/119629962#Comment_119629962

Ah I won't complain, it just looked like the movements being tarmacced the last while would open first. I'll trust they know what they're doing.

So after m8s to n25e opens, and n25w new alignment to tunnel, it seems like n8e to glounthaune is next alignment or maybe n40n to n8e. Anyone any guesses for after that? Would it be in the plans for m8s to go to dumbell and back to tunnel to allow realignment of existing roundabout?

hans aus dtschl · 19-09-2022 10:09am

That's what I was guessing: use the new dumbell interchange to free up some space at the tunnel roundabout. In doing so, you can remove all traffic from the eastern side of the roundabout in one fell swoop!

Do you then move the N40n to N8n traffic through there, to allow the N25w to N8n work to progress?

veryangryman · 20-09-2022 12:04am

Is the speed of progress since first shovel went into the ground here decent?

Seems to be 2 years plus to do 1 junction. Yes I understand its major etc etc but Newlands didn't seem to take this long and that would have a similarish aadt

AugustusMinimus · 20-09-2022 1:03am

https://www.boards.ie/discussion/comment/119639916#Comment_119639916

Newlands Cross was a straight forward flyiver. This is an incredibly complicated built with previsos of having to manage traffic throughout the build and the fact that it’s being built on a bog.

As far as I know they are ahead of schedule.

cantalach · 20-09-2022 1:33am

https://www.boards.ie/discussion/comment/119639916#Comment_119639916

Newlands X was nowhere near as complicated and a tiny works area in comparison. Chalk and cheese.

hans aus dtschl · 20-09-2022 9:55am

https://www.boards.ie/discussion/comment/119639916#Comment_119639916

I thought you were going to say that the speed of progress is impressive!

I'm certainly impressed. The scale of this project is really significant.

AugustusMinimus · 20-09-2022 10:08am

They’re now surfacing directly under the new bridge outside the tunnel. New alignment must be opening sooner rather than later.

Chris_5339762 · 20-09-2022 10:36am

It'll be nice to have this done (N25W to N40W) but Id be very surprised if its freeflow at this stage.

If what looks like a temporary tie-in is done, the first set of lights as you come towards Dunkettle will have to be obeyed. The traffic from Little Island will still need those lights. They can't close that road until the new dumbell is done or at least partially done. You may even get temporary lights joining the N40 going into the tunnel from this sliproad under the bridge - because two lanes of traffic will still be coming from the current roundabout. It'll cause chaos if they are all punted into the right hand lane entering the tunnel because of a new freeflow slip coming from the N25. There has to be lights for now, surely.

That dumbell, surprisingly, really is key to it all.

KrisW1001 · 20-09-2022 11:53am

Yes: the dumbbell will be functioning as the main means of getting traffic across the east-west mainline while the works that need to break the current roundabout are done. That probably means (for example) cars from Tivoli for the tunnel will be brought under m8, over the dumbbell and back down into the tunnel.

That’s going to be really bad for traffic, but from the way the works are progressing, I don’t think it will be done until most of the major links are almost ready, except for the short sections that can only be completed with the roundabout stopped.

I could be wrong, but I don’t think this kind of phasing would be possible if that movement was a freeflow rather than a dumbbell - if that junction wasn’t a dumbbell, some other form of roundabout/gyratory road would have been needed to allow multiple traffic flows to be routed over the N25 at various times during the construction.

hans aus dtschl · 20-09-2022 3:52pm

Yes or else a "big bang" of some kind, with only the E-W traffic through the interchange for a short period of intense works.

That new Little Island interchange dumbell is kind of the "pressure release valve" for this project!

Chris_5339762 · 20-09-2022 8:38pm

Yeah, but unless they did it over Easter or Christmas there is no period that wouldn't cause absolute bedlam in the case of a Big Bang.

The volume going through the interchange is such that a "big bang" would have traffic backed up to Cobh, Glanmire, Cork itself and likely Kinsale Road at rush hour. It just isn't feasible.

hans aus dtschl · 21-09-2022 11:38am

Yep it would have been a nightmare. No question.

AugustusMinimus · 21-09-2022 1:53pm

Surfacing under the new bridge continuing today. I’d be amazed if the M8S to tunnel movement doesn’t transition to go under the bridge at the same time as the N25W to tunnel movement.

Interestingly enough, renders of the final junction maintain the slip into Little Island.

hans aus dtschl · 21-09-2022 3:50pm

Yeah that Little Island slip road being retained was always a weird looking one I thought. Maybe some kind of emergency tunnel-closed traffic flow needs it or something.

KrisW1001 · 21-09-2022 5:36pm

It’s needed as an escape-road for southbound traffic if the tunnel is blocked or drivers realise they’re not safe to enter. The other side of the tunnel has a matching escape-road that diverges from the northbound carriageway, loops over the tunnel portal and re-joins the southbound carriageway.

it’s always open, you can drive up around it next time you’re on the road...

cantalach · 21-09-2022 10:45pm

https://www.boards.ie/discussion/comment/119647314#Comment_119647314

Correct, but it won’t provide access to Little Island.

AugustusMinimus · 22-09-2022 1:35am

https://www.boards.ie/discussion/comment/119648557#Comment_119648557

Where will people be able to exit if they have to take this slip?

cantalach · 22-09-2022 7:17am

https://www.boards.ie/discussion/comment/119648836#Comment_119648836

Good question. One of the recent updates mentioned that the slip would be for emergency access only or words to that effect.

KrisW1001 · 22-09-2022 8:50am

It will still connect to the existing R623 as before (see red line below), so it will end up being a way in to the Hoffmann business park for traffic arriving from N8/M8, but its primary reason for being is as an escape route in case of accidents at the tunnel.

Chris_5339762 · 22-09-2022 10:30am

There'll have to be a barrier put up or something, otherwise people are just going to use it. These are Irish drivers we're talking about!!!

AugustusMinimus · 22-09-2022 11:34am

Would have drivers use it be an issue? Assume it would be fine as long as there a decent off slip.

Chris_5339762 · 22-09-2022 9:23pm

It would be very bad. Given that you won't be coming off a roundabout, and will likely be appoaching at about 60kmh, it'll be sudden. And also, because you won't be able to get into the correct lane on the roundabout first, there'd be diving across lanes. To get from the new M8S to N40 movement, to this old sliproad, will require crossing the N25W to N40 movement, in a very short space.

cantalach · 22-09-2022 11:19pm

https://www.boards.ie/discussion/comment/119649129#Comment_119649129

Interesting. It’s not show in any of the movement diagrams, e.g. https://www.dunkettle.ie/media/1336/traffic-movements_from-m8.jpg

KrisW1001 · 23-09-2022 8:43am

It shouldn’t be shown on those diagrams: It’s one way only, and it’s only really useful for two estate entrances into Little Island, much like the existing off-slip. For everyone who doesn’t work in one of those two sites, it’s irrelevant.

Mushy · 23-09-2022 12:09pm

Was wondering would we get updates on openings in todays email, but seems it'll be next week. Seem to want to push the northbound traffic a bit West,assume that's to allow for piling of the remaining bit of a bridge for n25w to m8n happen

N8/N25/N40 - Dunkettle Interchange [open to traffic]

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