N8/N25/N40 - Dunkettle Interchange [under construction]

Chris_5339762

Thats what I thought and presumed (with the Little Island and Tivoli traffic merging into them before the tunnel).

But the gantries put up at Little Island West are suggesting that there will be two N25 lanes going into the tunnel, so that traffic coming from the M8 will have to merge into the tunnel stream, and from the "wrong"side of the road too - ie: into the right hand lane in the tunnel. I don't think this will work terribly well. I could be wrong, and it could just be a temporary and/or a terrible gantry though.

To this day I've never seen images or a model that show CLEARLY what the lane arrangements are on the upgrade.

Shedite27

https://www.boards.ie/discussion/comment/120446996#Comment_120446996

There's some plans here that show you what happens.

http://n8n25dunkettle.jacobs.com/docs/32102066%20Dunkettle%20EIS%20VOL%203%20Figures%20-%20Fig%201.1.1%20to%20Fig%202.4.1.PDF

Traffic from Tivoli merges into the traffic from Fermoy under the flyover to create one lane, that flows straight into the right lane of the tunnel.

Traffic from Little Island merges into the traffic from Midleton to create one lane, that flows straight into the left lane of the tunnel.

Everyone should then stay in lane until they're through the tunnel

KrisW1001

You can see it from the drawings if you look carefully, but here’s an unrolled version of what I think it’ll be. Note that traffic from M9 Dublin is never required to change lane (but if they want to exit at Mahon on the other side of the tunnel, they could move left here)

There is no passing or lane-changing permitted in the Tunnel, but there is a short bit where traffic that had joined from the city could move right to accommodate traffic joining from N25.

Shedite27

https://www.boards.ie/discussion/comment/120447561#Comment_120447561

Going by the drawings, the lane you have "from City" joins into the bottom lane. There's only one lane then between the two junctions you've drawn. "From N25" then has the top lane to itself in the tunnel

KrisW1001

My mistake - (what I thought was a second lane on the CAD drawing is actually a median strip between the Northbound lane and Southbound). M8-from-City and M8-from-Dublin merge down to one single lane, and then a second lane carrying N25 traffic joins beside that one.

https://www.boards.ie/discussion/comment/120446158#Comment_120446158

... so yes, you’re correct :)

_Kaiser_

https://www.boards.ie/discussion/comment/120357391#Comment_120357391

That looks ridiculous for what is the exit to a motorway. Bad enough them reducing it to one lane on approach for the tunnel as it is.

Kermit.de.frog

Completely agree. This is how you do a junction. All we get in Ireland (and Europe) is second rate tat. Which is why we are falling behind. Don't think or build big enough.

cantalach

https://www.boards.ie/discussion/comment/120453426#Comment_120453426

It’s not really reducing to one lane. The southbound M8 has two lanes. With plenty of advance notice, it will split into two free-flowing single lane links. One link will go east for Waterford and the city centre, while the other link will go south for the tunnel. I’m thinking that each link will carry a broadly similar number of vehicles so there won’t be any loss of capacity because half the number of vehicles will have half the number of lanes. The only downside is a short distance where there isn’t a second lane to allow the galactically impatient to overtake. I’m ok with that. It’s probably going to be 60-80 through the interchange anyway.

confidentjosh

https://www.boards.ie/discussion/comment/120453453#Comment_120453453

Ha ha, are you living in the real world at all? You should've had a good long think before posting garbage like that. Do you not see a) the size(footprint/land take) of that random junction and b) the enormous cost building something of that scale would amount to? No, of course you don't.

Cork despite its growing size is still a small to medium sized city in European terms and in world and US terms would not be considered more than a large town. The new junction layout will I'm sure be more than appropriate for the traffic levels that will use it as the road designers would've designed the layout with the current and future/growing traffic levels in mind.

Kermit.de.frog

https://www.boards.ie/discussion/comment/120453499#Comment_120453499

You lack confidence, like all Irish people. Not deserving. Of course an interchange like that should be built, and all junctions turned in to cloverleaf junctions a minimum.

The problem the Irish have is a lack of ambition.

Let me ask you a question - do you ever look up at night to the stars? Do you ever think about what got humanity to the moon? Imagine if we all thought like you. Do the minimum. No ambition.

Thank god for the United States.

mcburns07

https://www.boards.ie/discussion/comment/120453555#Comment_120453555

The roads in the states are very very poor.

cantalach

https://www.boards.ie/discussion/comment/120453555#Comment_120453555

Truly one of the more bizarre posts I’ve read on this thread. First you do some armchair psychologist thing on another poster which you then extrapolate to an entire nation. And then you display woeful ignorance of road design by saying that we need clover leaf junctions. Nobody builds them anymore because of their high land take and low safety. The junction in your photo is NOT a clover leaf.

AugustusMinimus

https://www.boards.ie/discussion/comment/120453669#Comment_120453669

The photo shows a stack.

Cloverleafs are generally not built anymore because the design results in entrance slips followed by exits which cause all sorts of weaving issues.

Stacks or partially unrolled cloverleafs are preferred. The latter is a half way house between a stack and a cloverleaf.

I believe the intended M20 - M40 junction is a partially unrolled cloverleaf.

_Kaiser_

https://www.boards.ie/discussion/comment/120453464#Comment_120453464

It's piss-poor design is what it is just as the intended M8-city routing is a mess.

Go East to hit 2 roundabouts and then merge back onto the inbound lane? How is that any improvement on even the current setup for that routing?

It's clear that anyone coming from the M8 is an afterthought - it's already bad enough with cars trying to skip the queue and switch lanes for the tunnel at the split at times.

confidentjosh

https://www.boards.ie/discussion/comment/120453555#Comment_120453555

🤣 This is a truly unhinged and laughable post. Irish people insulted as well as god and the stars talked about here in relation to a road junction. What a weirdo you are. Piss off back to some MAGA forum where you belong.

AugustusMinimus

https://www.boards.ie/discussion/comment/120455058#Comment_120455058

On your last point. How else can they have this junction free flow but have 2 M8 lanes feeding into the tunnel. I don’t think it’s possible.

Queuing issues will resolve when the full junction opens.

sheff_

I think for m8 - City Centre traffic the logical route becomes tunnel - south ring - south link.

Not sure if much of the traffic along the lower road/tivoli is of m8 origin/destination, but any reduction there would be a nice side effect of the convoluted m8-tivoli routing

AugustusMinimus

There is no way I would take that route furling rush hour. You’ll be fighting traffic at the following locations:

• Douglas flyover
• Kinsale Road Roundabout
• Queuing on the South Link road

Suspect it would be much faster to go in the lower Glanmire road (dependent of course on your final destination.

sheff_

This is true. The rush hour tivoli route though is 3 roundabouts followed by a crawl the whole way up to town (especially if half the tivoli dual carriageway becomes bus lane). So no great option.

Out of rush hour the south ring - south link will be much less hassle to any destination beyond tivoli.

AugustusMinimus

https://www.boards.ie/discussion/comment/120457375#Comment_120457375

We don’t know yet how the first 2 roundabouts will look like. I’ll hold judgement on these until the junction is in its final layout.

Traffic on the SRR is going to get worse when Dunkettle becomes free flow. Much worse I’d imagine.

KrisW1001

I don’t think SRR will get worse eastbound, because it’s the current Dunkettle interchange that creates the delays we see now. Westbound, I don’t see much problem either - more or less the same amount of traffic will be entering the tunnel as before, only now it won’t be bunched up into platoons by traffic lights north of the tunnel.

We can’t really judge the final interchange by looking at the throughput of what is effectively a building site: when the Tunnel-to-City slip finally opens, we’ll get a better idea of Eastbound, but Westbound might have to wait until the whole thing is done..

Of course, there will be an induced demand effect when the new interchange is in place, but removing the lights at Dunkettle will increase the throughput of the interchange enough to deal with this.

(Next step is to improve public transport to avoid us being back in the same kind of congestion in a couple of years from now)

AugustusMinimus

I think the throughput into the tunnel will increase, leading to higher peak traffic on the SRR. This will result in worse traffic but for a shorter period of time each morning and evening IMO.

People on here said that the Bandon road and Sarsfield Road flyovers wouldn’t cause any additional congestion westwards on the SRR. They were wrong with tailbacks before the Douglas Flyover becoming a daily occurrence when they opened.

I think the Douglas flyover will see serious congestion when all movements into the tunnel become free flow. 8 to 9 each morning will be chaos.

Shedite27

https://www.boards.ie/discussion/comment/120458006#Comment_120458006

What do you think will cause the extra traffic into the tunnel? The exta roundbaout that traffic from N8 -> Tivoli are subjet to? Think of the before and after for that traffic.

Before: Queue N8 southboung to meet the lights at the old roundabout. Then on the roudnabout, they were usually stopped again at red light where they meet the traffic coming out of the tunnel.

After: Free flow from N8 to first dunbell roundabout. At first roundabout they need to stop if there's traffic coming from Little Island or East going to Glanmire/East (fairly low volume I'd imagine). At second roundabout they never need to stop, only scenario would be if a vehicle leaving LI is doing a 180. Realistically that's free flow.

So they skip queing for 2/3 sets of lights to potentially stop at one quiet roundabout. I realise it's longer as the crow flies but it's going to be much faster IMO

AugustusMinimus

I don’t believe there will be additional traffic. However, I do believe the capacity of the junction will increase and so the current queues up the M8 and the N25 will be moved on to the Douglas Flyover. Hell, the queues back from the Bloomfield / Douglas Flyover could go as far back as the Dunkettle Interchange itself.

This was discussed a lot in the thread on the Bandon and Sarsfield Roundabout flyovers. In the end, traffic which was previously queued at these roundabouts got moved onto the Douglas Flyover with constant queuing there in the evenings eastwards.

Chris_5339762

https://www.boards.ie/discussion/comment/120458892#Comment_120458892

I've said that since Day 1, that the Douglas Flyover westbound will be badly jammed westbound in the mornings once Dunkettle is done - as the bottleneck will move to there.

I also fear that when the M28 is done and the bottlenecks caused by the N28 are gone, that the Douglas Flyover westbound will be one of, if not the worst bottleneck in the country with near constant jamups. I think when we get to that stage that we'll get armageddon.

The annoying thing is that one mile of widening between the M28 junction westbound, over the flyover (somehow) and to the Kinsale Road Junction would cure it. But thats going to be a very, very hard mile to widen, if ever. Don't forget the KRR bridge was built with 3 lanes westbound in mind. Its wide enough.

AugustusMinimus

https://www.boards.ie/discussion/comment/120459888#Comment_120459888

I think we’ve both discussed this at length in the M28 thread. The only workable solution I think is to stack carriageways on top of each other over the Douglas flyover. And that’s never going to happen.

Ideally, you want to cap the number of cars going through any stretch of road. There is a speed which maximises capacity. Once you go above that, chaos ensues. Traffic hitting the flyover over a longer period is a much better result than traffic hitting it in a more concentrated matter. The latter is just much worse overall.

Chris_5339762

I remember we have. My idea was to remove the current westbound slip at the M28/N40 junction and continue the slip on its own bridge, next to the N40, next to the Douglas viaduct and straight into the weaving lane between Douglas and the KRR. Then throw a third lane over the KRR bridge which nicely merges into the extra lane there. Its remarkably neat, easy to build and would solve the problem completely.

Jayuu

Good grief - the amount of doomsayers on this thread is just incredible. To listen to them we'd probably have been better off just not doing anything at Dunkettle.

Perhaps there will be issues at various points further along the routes because of increased demand although with throughput being delivered on a more even basis then hopefully some of these congestions points will ease out. In the end there may need to be futher improvements on the Cork SRR network but we can't simply deliver every single possible solution at once. Let's get Dunkettle done and see what actually happens as opposed to crystal ball gazing.

AugustusMinimus

https://www.boards.ie/discussion/comment/120461704#Comment_120461704

I don’t think anyone is saying Dunkettle shouldn’t be done. There’s no point in people sticking heads in sand over the likely consequences though.

hans aus dtschl

https://www.boards.ie/discussion/comment/120457179#Comment_120457179

Yep absolutely. They're effectively solving the Dunkettle interchange problem by partially routing traffic through Glanmire. I think this is not good.