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

hans aus dtschl

https://www.boards.ie/discussion/comment/121823609#Comment_121823609

Wasn't it the most expensive project in the state at that point though? I heard that they agonised over it, and cut the middle tunnel bore to nothing because they were so worried about the cost.

Cookiemunster

https://www.boards.ie/discussion/comment/121824215#Comment_121824215

Middle bore? It's an immersed box tunnel. The the 4 lane concrete sections would have been poured on land, floated out onto the Lee and then sunk into their final position in a pre dug trench. There was no boring.

RetroEncabulator

I have to say the route in from the N25 to the N40 / Jack Lynch Tunnel where you have to do that merge with the traffic coming in from the M8 is absolutely horrible. I was coming in on it late a few evenings ago and someone came down at way faster than the speed and started flashing and beeping at people who were mid-merge.

I'd hate to have to see traffic lights going back on, but if they don't do something about the speed on that junction e.g. with serious permanent speed cameras, they're going to start seeing accidents.

If they put up some permanent speed cameras and ANPR on that junction it would run completely smoothly. It just needs a ton of fines issued. There's no need to break the speed limits on it. Some of them are a bit conservative, but it's literally going to slow everyone down if there's muppets cutting people off and preventing merges.

RetroEncabulator

https://www.boards.ie/discussion/comment/121824275#Comment_121824275

From what I have read about the project, they created a dry dock which I think was where the GAA pitches are, just beyond Blackrock Castle. The sections were cast, and the ends were sealed / plugged. Then the dry dock was flooded, and they were floated into position. They sink the sections in to a pre-dredged trench, but I don't think they flood the interior with water at any stage. There may be some buoyancy chambers that were flooded with water that form part of the structure and the rest would have involved heavy ballast. They're just placed into line, sealed and grouted up etc, and then there's very heavy ballast placed across the top and the river bed is reinstated.

It's basically a massive dredging exercise.

The dry dock area was then reclaimed as GAA pitches and the walkway.

_Kaiser_

https://www.boards.ie/discussion/comment/121824281#Comment_121824281

I could be wrong but traffic merging should end up in the left lane of the tunnel and not impact on traffic inbound from the M8 unless they're trying to cut across into that right lane - in which case said flashing and beeping may have been entirely justified as many people do so regardless and (especially in Cork in my experience) without any use of indicators.

RetroEncabulator

https://www.boards.ie/discussion/comment/121824310#Comment_121824310

There's definitely a merge involved on one of those connections.

It's not on google maps yet, so I can't show it, but there's a left lane that ends and shoves traffic into a merge.

The merge from Dunkettle onto the M8 is also very short.

I think the whole thing needs speed cameras that limit it to about 50-60km/h just for the interchange itself, not the straight parts.

If everything's moving at a gentler speed, it will all flow nicely.

_Kaiser_

https://www.boards.ie/discussion/comment/121824317#Comment_121824317

Fair enough.. Bad design then caused by a compromised overall solution but compounded by unfamiliarity/inattention/impatience/ignorance.

hans aus dtschl

https://www.boards.ie/discussion/comment/121824275#Comment_121824275

Look up the definition of the word bore.

And the rest of your post is also inaccurate. It is not a 4-lane concrete section but a 2+1+2 lane concrete section.

I was told that the middle bore was reduced in size from the original design, but I have no evidence that they had ever properly considered a reasonable size for that middle bore. Also, I don't know what they were doing with the access road to the South of the tunnel management building, but would love to know.

RetroEncabulator

https://www.boards.ie/discussion/comment/121824336#Comment_121824336

You could deal with the impatience easily enough though with a few cameras and automatic enforcement. Overall the benefits to traffic flow would be quite significant and it would avoid a lot of stupid nonsense with potential minor bumps clogging it up.

RetroEncabulator

https://www.boards.ie/discussion/comment/121824336#Comment_121824336

Ultimately, you'd be far better off at this stage trying to reduce the traffic volumes on the N40 by spending money on something like a tramway to Carrigaline and through some aspect of Douglas. It may not be entirely justifiable at the current populations, but given the way things are developing, it won't be long until it is.

The tunnel's not going to go beyond 2 lanes each way and widening the N40 isn't really feasible either.

Given the city's population there's far too many cars using that route, with just really indicates a total lack of alternatives at present.

The transit planners also need to look at where people commute to and from. It's not just the city centre. There probably needs to be be a transit interchange on Little Island for example. That should be a major hub on the bus network but isn't.

Same applies to a few other places like that which are huge centres of employment with quite weak public transport or notions that people are going radially all the time, which clearly isn't the case. There's a lot of traffic going orbitally around from residential areas to industrial estates and business parks, basically following the major road routes. Mahon / Little Island / Ballincollig / Carrigaline which could definitely make use of busses to reduce volumes. All of those should have solid bus services.

hans aus dtschl

https://www.boards.ie/discussion/comment/121824310#Comment_121824310

No unfortunately there's a merge alright, and I've seen similar impatient behaviour from people on the M8 tailgating the cars ahead of them etc, and refusing to allow a merge from the N25. As the previous poster said there might need to be some enforcement here unfortunately.

RetroEncabulator

https://www.boards.ie/discussion/comment/121824377#Comment_121824377

I don't know what the fear of using a few speed cameras is though. They're completely reasonable to use in a situation like that and it's not a major imposition. Traffic lights or anything to block the junction would effectively render the whole rationale behind the project pointless.

It's the same on the M50. There are certain drivers are just making it worse by driving too aggressively. All this variable speed limit stuff is fine and well, but it's pointless without enforcement.

Couple it with good signage about avoid stopping, drive smoothly, merge like a zip and everyone gets through faster! Impatience slows everyone down!

Cookiemunster

https://www.boards.ie/discussion/comment/121824338#Comment_121824338

And where, pray tell, is this middle lane?

Whats in the middle is a pedestrian escape route. Not another traffic lane. It was built exactly as it was designed.

DylanQuestion

https://www.boards.ie/discussion/comment/121824373#Comment_121824373

I definitely think there needs to be more connections between Carrigaline and other parts of the city via bus. Right now the only buses are the 220/220x and 225, connecting the town to Ringaskiddy, Cork Airport, Douglas, City Centre, UCC, Model Farm Road, Ballincollig. There is no direct northside connection, no connection to Little Island, and the only connection to Mahon is by transfering to the 219 in Douglas. Douglas is essentially an interchange for Carrigaline. Bus Connects will fix this a bit by adding a direct northside connection (Apple) and interchanges in the City Centre to rest of the city. I still think that Carrigaline could support a direct route between Mahon via the N28 (Well Road is going to struggle to deal with multiple bus routes given it can barely handle the 219) and Little Island, though

niloc1951

https://www.boards.ie/discussion/comment/121824377#Comment_121824377

If we're talking about where the N25>N40 and M8>N40 come together before the northern portal of the tunnel, there is no merging provided for there.

Each lane is separated by a continuous white line the whole way through to the southern portal of the tunnel with 'stay in lane' painted on the road. Any lane changing should only take place after exiting the southern portal of the tunnel where there is over a km for drivers to get sorted before the Mahon exit (Jct 10) is reached.

cork_south

https://www.boards.ie/discussion/comment/121825747#Comment_121825747

I'd imagine people are referring to the merge onto the M8S via the loop from the Dunkettle roundabout direction.

Leatra

https://www.boards.ie/discussion/comment/121825756#Comment_121825756

I'm not blaming anyone in this thread, but the project team (and possibly others) have been woefully inconsistent in referring to that stretch of road. It's the N8, but it all gets wrongly lumped in as N25 sometimes.

AugustusMinimus

Actually, are all of the individual slip roads allocated a national route number?

hans aus dtschl

https://www.boards.ie/discussion/comment/121824457#Comment_121824457

As I said I don't have any evidence but was told was that the central bore was (at one point) considered as an actual pedestrian bore. How early this was in design I don't know, and have only been told this by someone working on it, and I haven't got documents from that early in the project. The few documents I have are all as built.

Edit: and I am in agreement that it was built as designed, that wasn't the point of discussion at all, we were saying that the design was whittled down to the minimum because the project was considered so big by the government at the time. People were looking at the original "simple roundabout" design and marvelling at how basic it was.

Edit: doing a bit of googling here and am surprised at the details I'm uncovering. Apparently the largest project by a local authority in the history of the state, and there was heavy pushback against it particularly on costs grounds. It looks like they really agonised over the design, bumping it from a 2-lane tunnel to a 4-lane one.

hans aus dtschl

https://www.boards.ie/discussion/comment/121825747#Comment_121825747

Sorry, we're not talking about the same thing here, it's the Tivoli to Mahon route we're discussing, if you can visualise that.

Hibernicis

https://www.boards.ie/discussion/comment/121824275#Comment_121824275

You appear to take issue with the use of the word bore. I’ll just leave this here; you might find it educational:

General Tunnel Information

The Tunnel is 620 metres long

There are six emergency exits in each traffic bore for pedestrians that lead into the central bore (pedestrian exit), the exit doors are at each end of the central bore

There are twelve emergency panels in each traffic bore that have hose reels and fire extinguishers

There are six emergency exits in each traffic bore for pedestrians that lead into the central bore (pedestrian exit), the exit doors are at each end of the central bore

Fans will pressurise the central bore to prevent smoke entering the central bore when an emergency door is opened

Lighting within the central bore (pedestrian exit) will fully turn on Approximately ten seconds after a door is opened

The first emergency telephone within each bore is 50 metres into the Tunnel and every 50 metres thereafter

There are fifteen emergency telephones within the North bound bore, approach and exit ramps

There are fourteen emergency telephones within the South bound bore, approach and exit ramp

Source: https://jacklynchtunnel.ie/general-tunnel-information/

Hibernicis

https://www.boards.ie/discussion/comment/121824305#Comment_121824305

Good summary. The casting basin (dry dock) was enormous. A public viewing platform was constructed adjacent to Ringmahon road and it attracted a lot of attention. I didn’t live in Cork at the time but it was obligatory pitstop any time I was in the area. The tunnel elements were sealed at both ends and floated into position and then lowered into the trench. There is a great arial photo here showing the tunnel elements after the castin basin was flooded, but before they were towed into position. No Dronehawk back then.

Picture source: https://cases.ita-aites.org/search-the-database/project/140-river-lee-tunnel

Further photo of the first tunnel element with buoyancy attached being floated into plac. Tthe northern portal section had already been floated and positioned at this point. Note the beginnings of what is now the N40 in the background, and all the grass in Mahon.

Picture source: https://www.facebook.com/oldphotosofcork/photos/a.425019591263720/427120851053594/

Hibernicis

https://www.boards.ie/discussion/comment/121824338#Comment_121824338

I’m not sure that the central bore was ever planned to be anything other than an emergence escape route. Access and egress would be problematic if it were to be used as a pedestrian route under normal circumstances. The fact that the tunnel got built was a result of an amazing series of coincidences and the efforts of some extraordinary individuals. And it had a very narrow escape….. It was planned as a two lane tunnel (one lane in each direction) and went through the feasibility study and public enquiry as such. In order to drag out making a decision, the then Minister for the Environment (Mayo’s finest, the one and only Pee Flynn) ordered a second public enquiry and the outcome was an increase to four lane tunnel. Doesn’t bear thinking about the consequences had the original plan been pursued.

DylanQuestion

Although I was one of the people to walk (or be walked) through the tunnel on completion, I don’t remember it. How was the planning process around the tunnel? Did it drag on for years and years with debates about slight details? Were there many objections? It probably helped that there was probably nothing in terms of houses nearby east of Bloomfield at the time. It’s crazy that for such an old city, most of Cork’s growth has been since the 1950s

AugustusMinimus

https://www.boards.ie/discussion/comment/121826692#Comment_121826692

Your last comment is the same for every Irish city. Huge growth in all Irish cities due to both urbanisation and general population increases.

I would say that the likes of Limerick, Galway and Waterford have experienced even more rapid growth since the 50s than Cork did. Cork has a much larger old core than those cities.

marno21

I think in hindsight, had it been built as a two lane tunnel we'd have got a massive Westlink style upgrade during the boom years. It might have been done right the 2nd time to the point that the current Dunkettle setup might have been emulated back then like the M50 upgrade.

The tunnel now represents a massive single point of failure on the Cork strategic road network. Rather than any talk of widening it a northern Lee crossing with city bypass is the only long term solution. Were the tunnel to be widened it would just put too much pressure on the Douglas flyover, KRR & N22 at Ovens.

Hibernicis

https://www.boards.ie/discussion/comment/121826692#Comment_121826692

We are a bit off topic, however if it weren’t for the Rive Lee Tunnel there would be no Dunkettle Interchange, certainly not in its current form.

Cork in the mid 80’s was a severely depressed economic wasteland. Fords, Dunlops and Sunbeam all gone, no IT industry and the pharma sector was really just beginning to be more than the original 1969 Pfizer plant in Ringaskiddy. And the rest of the country wasn’t much better. The general consensus was that the country was broke and unlikely to change. The height of our industrual ambition was Willy McCarter’s FOTL in Donegal employing 3,500 making tee shirts and underpants. The Collins and De Valera bridges had just been opened (allegedly the first “non-replacement’ bridges built since the foundation of the State) and despite their small scale were regarded with awe. The state’s motorway network consisted in its entirety of the Naas Bypass, all 5 miles of it.

So when talk started about Cork getting a “downstream crossing” as it was referred to, with a high level bridge or a tunnel at Tivoli being the options, Cork people took little notice, regarding it as kite flying and having little or no chance of proceeding. And anybody outside Cork (i.e. Dublin and Kerry) regarded it as “notions” if they thought about it at all. There was no NRA or TII at the time, so no coordinated approach to planning and prioritising the development of the National Road Network (Shout out to Eamonn for bringing us back to this) so it was up to the local council to try to make things happen. It’s difficult to convey the lack of interest and skepticism that attached to the prospect of the bridge or tunnel. The fact that it did get approved, funded and built is down to a small group of resolute and determined visionaries who took the idea and ran with it, and who by fair means and foul outmanoeuvred the competition (ever other Council and Region in the country and the Department of Finance) and got their project approved. There were also a series of happy coincidences in terms of timing, particularly in the political and financial arenas that allowed the project to “slip through”. So rather than objections, debates etc I think it’s fair to say that the public attitude went from total skepticism about the project in the early days utter disbelief right up to the opening. It happened at a unique point in time, just as an Old Ireland was disappearing forever and the Celtic Tiger was nothing more than lust in it’s father’s loins.

More here: https://en.wikipedia.org/wiki/Jack_Lynch_Tunnel

niloc1951

https://www.boards.ie/discussion/comment/121826168#Comment_121826168

Ah yes. Well that slip is just that and it has no right of way over the M8 which it's joining. Traffic joining from the loop is 100% dependent on the courtesy of drivers coming down the M8.

Unfortunately most drivers don't understand the concept of being courteous to others.

KrisW1001

@Hibernicis The largest factor was the EU Cohesion Fund that allowed Ireland to pay just 15% of the cost of the tunnel. The Lee Tunnel was one of the first schemes funded under this programme.

hans aus dtschl

https://www.boards.ie/discussion/comment/121826995#Comment_121826995

Of course, agreed, but we're saying that people are breaking the speed limit on the M8 section, preventing people from merging safely. Others are also tailgating (another result of them breaking the limit). We're saying there might unfortunately need to be some enforcement.