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Tunnel interchange discussion
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24-06-2011 8:42pm#1The National Roads Authority are inviting comments on the proposed new interchange
north of the Jack Lynch, so I thought it might be fun to have a discussion here too.
Their proposed options seemed needlessly complicated so I came up with my own.
Bear with me while I build the post - it could take a few minutes to pull it all
together. I swear I got a five year old to do the drawings in paint
Righty - first an overview. The current problems with the tunnel interchange in order
of severity are :
(1) A large volume of traffic travelling from the tunnel northbound to the east.
(2) A large volume of traffic travelling from the east into the tunnel southbound.
(3) A large volume of traffic travelling from the north (Dublin Road) to the tunnel
southbound.
(4) Traffic traveling from the city (west) into the tunnel southbound.
Solve even (1) and (2) and you'd probably have a massive improvement, but even though
it's not really mentioned, the fact that traffic on the main Cork-Dublin road passes
through that interchange as well is a concern. And it's going to be a bigger concern -
all signs are that the proposed dual-carriageway from Shannon to Rosslare via Cork,
will pass north of the city and link up with the N25 via the Dublin road. Effectively,
this means that in the future some of the Shannon to Rosslare traffic that currently
uses the bridge over the interchange, will then have to go through the interchange
itself.
Other concerns are of course space and budget. Between houses, commercial estates and
the Ibis hotel, there's not a lot of room to play with. The development I'd propose
would be built on mainly waste ground. Quite marshy waste ground, which we've never
been particularly good at building on in this country, but there have been successful
big construction projects on marshes in other countries so maybe we could learn and
improve. I'm also aware that it wouldn't be cheap, but compared to the complexity of
some of the proposals, I'd say mine would be a lot more cost effective.
I'll outline the four phases of what I'd do in four more posts. A quick summary is :
Phase 1 : Build a two-lane flyover east of the tunnel interchange to take traffic from
the Dublin Road to Cork City.
Phase 2 : Build a two lane flyover north west of the tunnel interchange to take
traffic from the city to the Dublin Road north/south. Also movie the northbound Dublin
Road west to make room.
Phase 3 : Build a two lane flyover north of the tunnel interchange to take traffic
northbound out of the tunnel to the east.
Phase 4 : Replace the roundabout by the tunnel management building with a t-junction.
Build a one lane flyover here to take traffic from Little Island west to Cork City.
[edit]New overview pic might show what I mean better, though it the East Flyover is missing from this one :
[/edit]0
Comments
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Phase 1 : East Flyover.
As in the picture - this flyover would start more or less where the turn off to Glanmire
East is now, loop up over the dual carriageway and rejoin just west of the PJ O'Hea
Opel dealership. Traffic travelling from the Dublin Road to Waterford would turn left
at the same spot it does now and follow the existing slip road onto the N25. Traffic
travelling from the Dublin Road to Cork would turn left, keep left and travel up over
the flyover to join the N25 Cork east of the interchange rather than west.
I can imagine a lot of people thinking to themselves that it makes no sense to do this
now and certainly no sense to do it first, but trust me - there's really no other way,
and this road will be needed in the future.
It might also seem very counter-intuitive for traffic on the Dublin to Cork road to
turn towards Waterford, but if it's well enough signposted it should be no problem.
I'd also work on the junction later on so that as soon as you're past the bridge
approaching the tunnel roundabout, the left turn splits off as soon as possible.
The big problem with this phase, apart from the obvious ****ty ground to build on, is
joining the N25 at that point. Basically you'd have the traffic heading from the
flyover to Cork and from the east to the tunnel crossing each other in a relatively
short space. I think it would be okay though - there is a good amount of room for
traffic to merge in.
We could make that easier by moving the N25 towards Little Island and bringing the
flyover down on the right of the N25 instead. This would increase costs and raise the
question of how traffic from the Dublin Road would get to Little Island west (I propose
to block off the ramp near the tunnel later)
I'm not 100% sure that this flyover needs to have two lanes. I'm not sure the traffic
now or in the foreseeable future will need them, but it'd certainly be cheaper to build
them not than add a second one later.0 -
Phase 2 : North West Flyover.
The purpose of this flyover is to take traffic travelling from the city away from the
existing interchange onto the Dublin Road north/south. Traffic going from the city
through the tunnel merges with the Dublin Road north of the tunnel and goes through the
interchange from there. Traffic going from the City to the Dublin road just merges
with the dual carriageway without going through the interchange.
As in the picture, this would start more or less where the old road is and loop around
to merge on the right of the southbound side of the Dublin Road. Again this is all
waste ground, but the northbound side of the Dublin Road would have to be moved West to
make room for the merge.
Ideally I'd like to merge far enough north that traffic from the city can still get to
the Waterford turn off and hence to the off-ramp for Glanmire East, but I think it
wouldn't be possible. I think anyone wanting to do that would be boned.
I also realise there'd be a lot going on in a short space of time with traffic from
Dublin having to merge with traffic on their right, within a few hundred yards of
traffic for Rosslare splitting off to the left, but I think it could be managed.
And if anyone's wondering - I'm not missing the obvious that I now have twice the
traffic approaching the interchange from the north. I'd address this some bit by
altering the timing on the lights (I'd now have no traffic coming from the west), but
in reality I'd be aiming for phases 2 and 3 to be finished at more or less the same
time.
The obvious main problems are space and safety. I'd like to loop further north than
I've indicated in the picture, but I'm not sure if that land is available. I'd also
propose slowing down the Dublin traffic before it gets to that point. In reality, this
happens already and when traffic is heavy you'd be crawling at the point anyway. I
think with proper signage it could work.0 -
Phase 3 : North Flyover.
As in the picture, this starts north of the current interchange, and using the existing
dual carriageway exiting the roundabout, the flyover loops up over the southbound
Dublin road to the east, over the flyover from phase one and merges with the N25
eastbound more or less where the existing ramp from Glanmire east merges with the N25.
Obvious problems with this one are space and the ground. There's not much room to
begin the flyover before clashing with the North West flyover, and all the ground I
propose building on is marshy.0 -
Phase 4 :
At this point the tunnel roundabout will cease to be a roundabout - traffic will flow
through it north-south only.
From the tunnel : Traffic going to the city will just turn left onto the existing ramp.
Traffic heading north for the Dublin Road will just continue straight through.
Traffic heading east will turn right onto the flyover and join the N25. Traffic
heading to Little Island West will have to use a ramp (purple) to loop back around and
turn left before getting back to the tunnel.
To the tunnel : Traffic from the east will use the existing ramp and merge with traffic
on their right entering the tunnel. Traffic from the north will just continue straight through. Traffic from the west will merge north of the current interchange on the
right of the Dublin traffic.
The roundabout would be blocked off, as would the ramp to Little island West
approaching the tunnel. The East ramps would be smoothed out to make it easier for
traffic to merge. Traffic from Little Island West might get it's own flyover to take
it over the dual carriageway to link with the ramp to the west, but if the budget
doesn't allow, they'd be boned. The roundabout outside the management building would
be replaced with a T-junction.
Traffic from the Dublin road going east just turns left onto the existing ramp and
merges with the N25.
Traffic from the east going to the Dublin road.... is boned! Honestly (not that this
isn't all pure fantasy anyway, but) I don't think the budget would cover it so I left
it out, but I'd propose a 4th flyover, going from the end of the East Flyover,
over/under the North Flyover, over the Dublin road to merge on it's left. Again, I
think a single lane flyover would do. I think this is the least critical traffic flow
so to cut costs I'd be tempted to ignore it and force the traffic to go to the around
the Dunkettle roundabout and use the North West Flyover. For the sake of completeness,
here it is :
So what do ye think? Probably a complete waste of time to do all this but I enjoyed
the mental exercise
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Blitzkrieger wrote: »
The whole need for an upgraded junction is to make it freeflow and get rid of the traffic lights and the roundabout. It looks like from your plans that the roundabout would remain and consequently some traffic lights would still be needed. Also you seem to building right on top of the train line which is another problem. The reason the NRA's plans are complicated is because making two existing intersecting motorways free flow is actually a difficult process.0 -
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two wheels good wrote: »And I've often thought playing golf in shopping centre would be fun. Very anti-social though.
Even assuming the ethanol were produced from food byproducts or algae and not a soya ranch in the Amazon, E85\ E95 can only be though of as more environmentally friendly in the same way that a kick on the shins could be considered more friendly than a head-butt.
Nah, still too close to speeding traffic and not much protection. Haven't you noticed the idiots blithely crossing the central solid white line in the tunnel.
Kicks on the shins & golf in shopping centre? things are starting to not make sense now
Ah feck it they could just drill another tunnel beside it for cyclists and horses. No doubt it would become a 'shooting galley', gallery or alley. Joe Duffy wouldn't agree with it either. Maybe we can have a cable car across the lee instead, though no doubt that will attract it's fair share of complainers too
Can't say I've noticed any idiots in the tunnel. Maybe they come out only at a certain time?0 -
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