N40 - Cork South Ring Bandon & Sarsfield Flyovers

top floor

AugustusMinimus wrote: »

I presume the only piece that will be limited is slip lane going onto the Sarsfield's roundabout ?

If that's the case, I wouldn't think it should make a huge amount of trouble. If you wanted to, you could continue onto the Bandon roundabout and do a 360 there to access Wilton.

Possibly better to do a 180?:)

murphym7

AugustusMinimus wrote: »

I presume the only piece that will be limited is slip lane going onto the Sarsfield's roundabout ?

If that's the case, I wouldn't think it should make a huge amount of trouble. If you wanted to, you could continue onto the Bandon roundabout and do a 360 there to access Wilton.

I think where we will see the trouble (outside of the Sarsfield slip obviously) is the extra volume using the Bandon roundabout instead.

alaimacerc

Some closures on SRR this evening: left hand lanes of the southbound entrance, and the corresponding segment of the roundabout. Possibly restoring footpath access?

kub

top floor wrote: »

Possibly better to do a 180?:)

No a 180 will only put you on the slip heading west from Bishopstown. He is correct as you will be coming back in the direction you came in therefore 360 degrees.

Ludo

kub wrote: »

No a 180 will only put you on the slip heading west from Bishopstown. He is correct as you will be coming back in the direction you came in therefore 360 degrees.

:eek:

xabi

kub wrote: »

No a 180 will only put you on the slip heading west from Bishopstown. He is correct as you will be coming back in the direction you came in therefore 360 degrees.

You might want to dig out one of these

top floor

kub wrote: »

No a 180 will only put you on the slip heading west from Bishopstown. He is correct as you will be coming back in the direction you came in therefore 360 degrees.

Actually a pretty subtle (and potentially confusing problem).

The assumption of 180 deg. turn being necessary is based on the convention that the driver heading straight ahead is initially on a 0 degree bearing. So a 180 turn would bring you straight back.

However on a roundabout the driver wishing to return will pass exits at 90, 180, 270 before choosing the one at 360. The reality though is that the driver was facing the one at 180 before entering the roundabout so only needs to add 180 to the initial bearing.

The illusion of 360 is actually a nice example of something, but I'm not sure what yet. It deserves to have a name. Anyone know it?

That's my angle on it anyway But I do see where you are coming from

xabi

Doesn't matter which bearing your heading, taking a 180 will send you back the way you came. I see where the confusion lies though, as a roundabout is a circle and 360 degrees around.

alaimacerc

top floor wrote: »

The illusion of 360 is actually a nice example of something, but I'm not sure what yet. It deserves to have a name. Anyone know it?

Geometry?

Look at it like this: if you measure the difference in angle between the two bearings (directions of travel, vectors, as you prefer) before and after (eastwards before, westwards after), it's 180 degrees. If you measure the difference in angle between the two positions, from the perspective of the centre of the roundabout, it's 360 degrees (AKA 0 degrees).

kub

alaimacerc wrote: »

Geometry?

Look at it like this: if you measure the difference in angle between the two bearings (directions of travel, vectors, as you prefer) before and after (eastwards before, westwards after), it's 180 degrees. If you measure the difference in angle between the two positions, from the perspective of the centre of the roundabout, it's 360 degrees (AKA 0 degrees).

That was how my brain calculated it.

Outkast_IRE

Hope the council do a proper walkabout before accepting handover, there is plenty of small issues with the foothpaths and subsidence already, the foothpath on the southside of the sarsfield rd rounabout has places where its sunk majorly and has cracked badly.

blindsider

Drove around the Sarsfiled Roundabout yesterday - it was quiet, so I drove slowly.

What a complete mess it is. There are at least 3 major dips in the road from the N40 exit to the Tesco exit. It's appalling. You'd wonder how they got is so badly wrong.

Excuses are completely unacceptable here - bog or no bog - SIAC are a big company with all the experience needed for this project.

http://www.siac.ie/siac/index.jsp?&1nID=93&2nID=101&pID=218&nID=556&aID=0

Let's hope Bouygues (SIAC's potential new owner) get in and do it properly this time.


Are there penalties etc associated with this? The project can hardly be called a success, so you'd expect some sort of penalty surely?

Outkast_IRE

Traffic is mental at the sarsfield roundabout with all the additional work they are doing digging back up the off ramp etc.

grogi

blindsider wrote: »

Excuses are completely unacceptable here - bog or no bog - SIAC are a big company with all the experience needed for this project.

Are there penalties etc associated with this? The project can hardly be called a success, so you'd expect some sort of penalty surely?

Don't jump to conclusions too fast.

The design and construction works were probably done by different bodies.
As long as the constructions were done according to the specifications, the contractor is not to blame.

blindsider

grogi wrote: »

Don't jump to conclusions too fast.

The design and construction works were probably done by different bodies.
As long as the constructions were done according to the specifications, the contractor is not to blame.

Fair point!

AugustusMinimus

Thread here stating that the extra slip roads to be added for Mahon have been shot down. Madness.

http://www.boards.ie/vbulletin/showthread.php?p=89636545#post89636545

kub

AugustusMinimus wrote: »

Thread here stating that the extra slip roads to be added for Mahon have been shot down. Madness.

http://www.boards.ie/vbulletin/showthread.php?p=89636545#post89636545

I could never imagine NRA allowing a slip from the back of Mahon Point to N40 tunnel bound.

It is on a bend, there is an existing slip a few hundred meters (if even that behind it), then there is the new barriers and the speed of the traffic on the road.

All I can imagine is some sort of reorganisation of the existing East bound slip road with a branch out of Mahon Point.

spacetweek

kub wrote: »

I could never imagine NRA allowing a slip from the back of Mahon Point to N40 tunnel bound.

Agreed. There's a hierarchy here - national trunk roads shouldn't facilitate entry and exit from a shopping mall. That's the job of local roads.

AugustusMinimus

spacetweek wrote: »

Agreed. There's a hierarchy here - national trunk roads shouldn't facilitate entry and exit from a shopping mall. That's the job of local roads.

Well. The NRA has 2 choices here. Either go along with the plan and improve traffic flow in the area or ignore it and watch as the traffic will again get progressively worse and worse as the economy starts to improve.

A hierarchy of roads shouldn't come before common sense.

grogi

spacetweek wrote: »

Agreed. There's a hierarchy here - national trunk roads shouldn't facilitate entry and exit from a shopping mall. That's the job of local roads.

But N40 is de-facto a local road now. It goes through the densely populated areas of the City...

What's more, just finished/broken/being fixed upgrades to N40 feature such entry to a mall... So precedence is already there

AugustusMinimus wrote: »

Well. The NRA has 2 choices here. Either go along with the plan and improve traffic flow in the area or ignore it and watch as the traffic will again get progressively worse and worse as the economy starts to improve.

A hierarchy of roads shouldn't come before common sense.

Yep - they can reject the reality or try to do something before the upgrade works become simply impossible.

AugustusMinimus

In truth, the N40 has never been a bypass or anything of the sort.

It is an urban motorway (for use of a better word) with maybe 60% of its traffic being traffic which commences in some part of the metropolitan Cork area and finishes up in another part of the metro Cork area.

The SRR cannot be compared to either the Limerick or Waterford bypasses. In both of these cases, there is a much higher percentage of through traffic accessing these bypasses.

I'm not sure what the NRA are trying to achieve by blocking these slip roads. In my mind, there is enough space for at least 1 extra exit sliproad. I cannot fathom what is the problem with the entrance slip road between Bloomfield and Mahon interchanges. Not a clue.

kub

All of what you are saying makes perfect sense, but just on the gap between the Bloomfield slip on and Mahon exit, is there enough space?

Just consider the occasional tail back on the Mahon exit, the speed of joining vehicles from Bloomfield, which can be slow especially with the future container trucks as well.

Is there a guideline somewhere of the recommended distances between junctions I wonder?

SpaceTime

Is there any way the exit capacity could be increased by adding extra lanes and a double-exit type setup similar to the merge say between the M7 and M8.

It might make more sense than adding an extra exit when there's really no space for one.

Alternatively, an extra slip way and bridge built further back from the tunnel to take traffic into Mahon Point on the other side of the retail park near where the pedestrian bridge is that takes the railway walk over the N40.

The City Council and Mahon Point would have to do something to re-organise the local roads though.

Live at Three

2 words: Monorail

alaimacerc

SpaceTime wrote: »

Is there any way the exit capacity could be increased by adding extra lanes and a double-exit type setup similar to the merge say between the M7 and M8.

I wasn't familiar with this, but I just looked at it online, and it looks pretty scary. Usual simple flyover arrangement, but two lanes, with the merge from the sliproad done with chevronning between the lanes, and slight separation along the length of the road. I wonder if that'd be possible even between two N roads, much less between a N road and an "access" road. (Not more than an R, I don't think?)

It might make more sense than adding an extra exit when there's really no space for one.

Better, though not necessarily good! Maybe the whole area needs to be uprated (or down-accessed).

Alternatively, an extra slip way and bridge built further back from the tunnel to take traffic into Mahon Point on the other side of the retail park near where the pedestrian bridge is that takes the railway walk over the N40.

Wouldn't that be very close, too? Unless your plan is to get rid of the existing junction completely, and have two new ones, well-spaced on either side of that location. Which sounds attractive on the face of it, if likely a tad dear!

SpaceTime

That setup is also done at the merge from the South Link (outbound) to the N40 Douglas-bound just after the Kinsale Road junction and it works.

In fact, they're are lots of close junctions there... Douglas East and Douglas West are very close together and followed by a narrowing to regular 2+2 dual carriageway for the overpass elevated section across Douglas village.

Don't really think that's much different to the tunnel and the junctions are even more complicated than any proposal for MP.

The M50 is the closest to the N40. They're both 100km/h DC with very frequent junctions.

The M-classification on the M50 seems to be more of a case of keeping cyclists etc off it ... Something that would be welcome on the N40..

I think a mountain is being made out of a molehill about this.

You've also got the option of extending the tunnel 80km/h speed limit back a km or so to cover the MP exits.

There's also a big problem where cars coming from the Carrigaline/Rochestown Rd direction via the Bloomfield Interchange are fed into a 3rd lane on the N40 that becomes the Mahon exit ... They end up trapped while fast moving traffic runs from the interchange into MP!

In slow moving N40 traffic when attempting to exit into MP, I've had undertaking cars on the slip road aggressively beep / flash me as they think they're safe to just drive along at 100 in parallel to a merge and block all exiting traffic from the N40..

Effectively, you can have to merge from a slow moving DC at like 50km/h if the tunnel is busy into a slip way with traffic running at 100km/h+ !

It's a pretty strange layout.

Ideally, they needed an extra single lane seperated from the DC by a barrier to allow that link from Douglas to MP without interfering with slip road traffic.

That would also take the Douglas/Carrigaline etc flow of traffic into MP off the N40 entirely which might be a big help at peak times too.

The whole junction setup needs a complete rethink.

Bear in mind that this exit is probably far busier than many exits to towns on major interurban routes yet, got planned really quite poorly.

There are similarly abysmal connecting links to Blanchardstown SC and Liffey Valley.

The only Mall that makes good use of multiple entrances is Dundrum Town centre. It has loads of carpark entrances that really spread the load and it's not straight off the side of a motorway.

grogi

SpaceTime wrote: »

Is there any way the exit capacity could be increased by adding extra lanes and a double-exit type setup similar to the merge say between the M7 and M8.

There are many different things that can be done, that would increase the junction capacity/reduce traffic.

a) Extend the left-turn-only lane on R852 southbound, up to the bus stop. If lack of space, get rid of the median on R852. This would allows much bigger volume go freely left, without waiting for the green traffic light ahead.

b) Add the exit from the shopping centre, but not directly to N40. Currently existing exist should be modified: two lanes go east for ~200m and merge into one. New exist should join now, keep two lanes for 200m and merge into one lane and finally join N40 yards ahead from the tunnel. This setup would provide enough space for queuing and allow avoiding blocking the traffic lights, feed only one stream of cars into N40 that had enough room to get speed and not disturb traffic on N40. The fastest lane on N40 should not be allowed to switch lane from right to left when this merge happens.

That's what I mean (A28 Northbound): http://goo.gl/maps/Iixcr

c) Modify the painting on the N40 eastbound when merging with the exit from MP. Fastest lane should not be allowed to change the lane left until the traffic from MP fully merges. Right now this place witnesses some very bad things...

wingfo

Why is it that on my new garmin sat nav with all the latest maps just downloaded, the new flyovers don't register on my device as it tells me take second exit off roundabout.

TheChizler

wingfo wrote: »

Why is it that on my new garmin sat nav with all the latest maps just downloaded, the new flyovers don't register on my device as it tells me take second exit off roundabout.

Contact garmin? They're officially still under construction, maybe they don't include incomplete works.

antoobrien

TheChizler wrote: »

Contact garmin? They're officially still under construction, maybe they don't include incomplete works.

I remember it took them several months to get the M6 into Galway mapped (which meant I missed my free update window).