N40 - Cork South Ring Bandon & Sarsfield Flyovers

Geogregor

Did they finish installing the beams?

Prowetod

Yeah. These were taken last Thursday.

MrDerp

AugustusMinimus wrote: »

On a closed system, this is easiest to visualize with a sand timers.

Picture 3 sand timers, stacked on top of each other. 3 squeeze points where sand has to go through at a slower rate. Each pinch point, is like a roundabout on the SRR.

Pour sand in the top. Sand will get lodged in the top part. It will slowly pour through the first pinch point. No sand will get back up at points 2 or 3 because the rate at which sand it coming through point 1 is the same as it can go through points 2 and 3.

Remove point 1 and the sand will backup at point 2. Remove points 1 and 2 and it will back up at point 3.

This obviously doesn't take account of

1. Each roundabout having slight different capacities or
2. That cars can exit or enter the SRR between the 3 roundabouts we are discussing in question.

To me, the tailbacks going east towards Dunkettle will simply have to get worse. However, as MrDerp has said, it doesn't mean it will take longer to get from Ballincollig to past the Dunkettle Interchange. However, it will probably take longer if you enter the SRR at either the Kinsale Roundabout or Bloomfield just to the backlogs now all being in front of you.

Argh. Can't resist.

You are still forgetting about time.

Lets define 'peak' as the time at which the arrival rate of cars is greater than processing rate of cars, i.e. system utilization is > 1 and the queue is growing on average over time

Lets imagine, for argument's sake, that peak at the dunkettle is currently 4.30pm to 5.30pm, and that it currently takes a car, leaving Ballincollig at 4pm, 30 minutes to get to the other side of dunkettle. i.e. they get through just as 'peak' begins, as above defined.

Now lets say that the upgrade of the two junctions, allowing for free-flow and some small slow down at the merge point, has shaved 5 minutes off each queue (it's not so bad at 4.10ish and 4.20ish, for arguments sake) so that the total time from entering the system at Bandon rd RAB to leaving Sarsfield's rd RAB has reduced from 15 mins to 5 mins.

Now more cars will arrive in advance of the old 4.30pm beginning of the peak. It will be some function of increased arrivals which have passed through one or both of the new junctions. So the arrival rate, to dunkettle, will reach capacity (processing rate, at dunkettle) earlier in the afternoon. Not by the full 10 minutes, but by some amount of that.

Also, the likelihood of finding cars [Pq, the probability of having to queue] already in the dunkettle system, from the tunnel side, has also decreased because the system had capacity (before the peak began) to process some cars which are now arriving to the system earlier.

So, the system at Dunkettle will in theory reach capacity earlier, but in doing so will also better utilize the pre-peak time as it will process more cars earlier in the afternoon. Those e.g. 50 drivers lucky enough to finish work at 4pm are no longer at the front of the queue at dunkettle, occupying one light turn, when the guy who finishes at 4.05pm gets to the system. Because they got there, and got through, earlier (if they came from afar).

This sucks for the guy who works in Mahon Point and leaves at 4.25 who can, from his perspective rightly, crib that "they only moved the problem down the road", because he used to hit the tunnel before the peak, or earlier relative to the start of the peak.

In short, the bigger arrival rate of cars from the system, to dunkettle, will now mean that dunkettle gets to work earlier in the day. The throughput will improve for everyone but those who get on after sarsfield's road during certain times.

It's all good.

As an observation, also, I would offer that many on here complained that Abbeyleix would get worse on a Sunday when the motorway sections of the M8 through Tipperary opened. There was talk of the old N8 "stretching out the traffic before Abbeyleix" and that the cars would all arrive quicker, making the tailbacks longer. This opinion suffered the same fallacy as people have here, which is that only the increased arrival rate to the system matters, when in fact one has to consider the earlier arrival time of cars also. People didn't time their journeys to get to Abbeyleix, they left at a certain time. Similarly, people will leave work at the same time, and will begin to arrive earlier at Dunkettle in the case of those coming from Sarsfield's rd RAB and beyond to the west.

AugustusMinimus

I see what you're getting at. However, surely this effect won't be that big ?

Purely personal observation, but queueing at the tunnel in my mind has got worse since the Kinsale flyover opened and there was prob more cars on the road before it opened than now.

MrDerp

AugustusMinimus wrote: »

I see what you're getting at. However, surely this effect won't be that big ?

Purely personal observation, but queueing at the tunnel in my mind has got worse since the Kinsale flyover opened and there was prob more cars on the road before it opened than now.

I can't comment really on that, as I don't live in Cork anymore and was never a daily tunnel user.

Perspective is everything here though. The tunnel appears worse for you, and the tailbacks longer. For many it could be shorter. Timing is everything. Some people will see a benefit - certainly overall someone driving from Ballincollig at 5pm now must now beat some cars getting from e.g. Bloomfield interchange to the queue. They could well see a 'shorter' queue. Whereas the bloomfield driver will be incensed.

Also, improved times attracts more drivers. I've used the m50 daily for 3 and a half years and I've seen my commute get busier. There was an initial boon following the upgrading, but now I've seen my morning commute get much busier, despite there being less cars on the road overall. I believe in the case of the m50, this is because:
- More cars are attracted to the route because of barrier free tolling removing a blockage
- More cars are attracted to the route because of the improved throughput (toll dodging now carries a more significant time penalty)
- More cars are tempted to leave later as the peak is nowhere near as busy, thereby gradually increasing the peak.

Driver behaviour will change with improved throughput. Everyone wants an uninterrupted drive ideally. I regularly spend 10 euro return on extra petrol and tolls using the m50 over surface streets, with no gain in time, because the drive is more pleasant.

I see your point though. There will be times when the queue is simply bigger, and incidents will cause bigger tailbacks more quickly. A crash on the m50 can lead to epic journey times, because there's so many extra cars filling 3 lanes and getting to the scene quicker. Bad days may well become worse.

Roll on the Dunkettle upgrade! Votes all round for the party that promises to upgrade dunkettle, start the North Ring road, and clear Cork Airport's debt. To hell with national issues :pac:

AugustusMinimus

MrDerp wrote: »

Roll on the Dunkettle upgrade! Votes all round for the party that promises to upgrade dunkettle, start the North Ring road, and clear Cork Airport's debt. To hell with national issues :pac:

I'd also build a Carrigaline road to Airport Roundabout connector road. Won't be happening anytime soon I'd say though.

http://www.boards.ie/vbulletin/showthread.php?t=2056832458

superhooper

Anyone know if the culvert under the now in place beams is going to be put in a pipe or fenced off and left open. At this stage I'd imagine they must be leaving it open.

Ambush Rebel 2010

superhooper wrote: »

Anyone know if the culvert under the now in place beams is going to be put in a pipe or fenced off and left open. At this stage I'd imagine they must be leaving it open.

I imagine they are going to leave this open.. From looking at some of the plans it appears that way.

phatmanwc

Great to see so much action on this thread (and obviously on the flyovers) recently, I am a long-term observer. Installation of the lighting on the Bandon Road flyover seems to have begun, with one or two of the standards in place. Will get a picture if I can.

Ambush Rebel 2010

Indeed, I think the next 2 / 3 weeeks should see a big update on the Sarsfields Flyover. Nothing stopping them now from pressing on now.

On another note has anyone seen the track machine working between sarsfields pitch and the togher exit(east bound). It has been there a while and note sure what it is doing...

Jayuu

Haven't been to Cork in years but I'm tempted to go once this project has completed! And I'm loving the discussion on bottleneck analysis.

xabi

Hopefully they line lane 1 up coming from Sarsfiled in the tunnel direction, with lane 1 going over the Kinsale flyover. Previously if in lane 1 you found yourself in lane 2 of the flyover meaning lane 1 was seldom used. Is this shown on any plans?

Ambush Rebel 2010

xabi wrote: »

Hopefully they line lane 1 up coming from Sarsfiled in the tunnel direction, with lane 1 going over the Kinsale flyover. Previously if in lane 1 you found yourself in lane 2 of the flyover meaning lane 1 was seldom used. Is this shown on any plans?

It would be great to see this being done alright.

That inside lane is very seldom used. I think users feel the will be 'trapped' by the two lanes of traffic exiting the Kinsale flyover and for safety sake staying in the 'middle' lane

My thoughts would be they could only increase it to three lanes once east of the Togher Exit which (Space permitting) would only increase the length of the 3 lane by a couple of hundres meters.

I stand open to correction though..

Good to see plenty of posting on the forum.

Roll on July!

Aidan1

Previously if in lane 1 you found yourself in lane 2 of the flyover meaning lane 1 was seldom used.

Usually I'd completely agree with you (and then I'd start giving out about people not using lane 1), but I think this might be slightly different (on the Kinsale flyover that is). There's often a lot of traffic joining the N40 Eastbound at the KRR junction, and the sightlines as you come over the brow of the flyover are not ideal - fine in normal visibility, but still not great. There may well have been a decision taken to deliberately keep traffic to the right and leave that lane as a quasi filter lane - either way it works quite well as it is.

xabi

Doubt it, if they didn't want people to use it they wouldn't have built it.

AugustusMinimus

xabi wrote: »

Doubt it, if they didn't want people to use it they wouldn't have built it.

1. 3 lanes each way future proofs the Kinsale flyover.
2. It allows for earlier merging into the lane to take either of the douglas exits.

xabi

They only have 3 lane going East though dont they?

AugustusMinimus

xabi wrote: »

They only have 3 lane going East though dont they?

The lane going west is designated as a hard shoulder. There'll be 3 lanes going west towards the Sarsfield's Roundabout once the works are completed. Will be interesting to see if they will change this hard shoulder to a lane.

Chuckler

Hi everyone, just started following this thread recently and have to get something off my chest. If I'm coming from Ballincollig heading east towards Wilton, does that mean when the dual flyover's are completed, I will have to turn off for Wilton at the Bandon Road Roundabout? Surely this can't be the case? Apologies if this has been previously discussed..

phatmanwc

I'm afraid so; it's to do with what are known as 'weaving lengths', and the issue of merging cars conflicting with diverging cars over a short distance. If the distance between the roundabouts was larger, this wouldn't be an issue. In terms of the merging movement winning out in this case, I'm sure it was based on recorded/projected traffic volumes, with higher numbers of West Cork originating vehicles heading eastwards than Ballincollig traffic diverging to Wilton, or something along those lines.

Don't worry, the roundabout will be a breeze when the flyovers open!

AugustusMinimus

I think the idea is that the Bandon Roundabout has been given complete access to the mainline due to it linking the N71 to the N40.

However, I suspect that the Wilton Roundabout might actually see more traffic. Not sure overall.

AugustusMinimus

By the way, here is the way around the weaving issue and still have 4 slip roads leading onto the mainline for both roundabouts.

I've drawn a fairly crappy design in MS Paint. So for the crapiness



Anyways. Red line is the mainline. Green is the slip road, leading off the mainline and onto the Sarsfield Roundabout. The blue line represents the slip road coming off the Bandon Roundabout and onto the mainline.

Elevation changes are something to keep in mind here. The mainline above each roundabout are quite elevated. So, the slip road to enter the Sarsfield Roundabout begins at the mainline's most elevated point going over the Bandon Roundabout.

Underneath, the slip road from Bandon Roundabout to mainline is completely at ground level. the green slip road begins at an elevated position on legs and takes it over the blue slip road. it then proceeds at ground level until it reaches the Sarsfields Roundabout.

To facilitate going from the Bandon to Sarsfield roundabout, you would follow the blue slip road and then the purple slip road and finally onto the green slip road.

As you can imagine, the same solution would be used on the South side of the scheme as well on the North side.

IMO, this completely gets rid of any weaving issues between roundabouts and means that the capacity would be higher than the current design.

Anyone foresee any issues with this design ?

phatmanwc

Just drove from Mahon Point to Wilton on the South Ring, first time in 4 years (been away), and I have to say, it's a very impressive stretch of road! Honestly, I had forgotten. Ok, it's got its flaws, but some great sweeps and vistas, definitely an interesting drive, as our dual-carriageways/motorways go.

One thing I have to mention is the lack of traffic management coming into the Sarsfield works; at the moment, everything is merging into a single lane coming into the roundabout, and there isn't a single flashing light, just cones and unlit arrows, which nearly resulted in a van rear-ending me. Think it's a bit lacking, might send off an email to that effect...otherwise, things shaping up nicely!

phatmanwc

AugustusMinimus wrote: »

Anyone foresee any issues with this design?

That would sort out the weaving issue. However, based on the grades, the green diverge would likely require a pretty lengthy section of elevated roadway to get back down to grade; considering there's already a diverge onto the Bandon Road Roundabout, heading east, it seems like slight overkill. However, not sure about the traffic volumes for this movement, but going on past experience on the South Ring, some definite foresight wouldn't go amiss this time around, and I just hope the Bandon RR is future-proof in this regard.

Bearing it mind it's just a rough sketch, the location of the blue-purple split seems a little close to the mainline. I'm thinking maybe run them on either side of the elevated green section, splitting them back closer to the BRR, and then continuing with two lanes (one purple and one green, say) to Sarsfield.

I seem to remember an early proposal at the Kinsale Road Flyover, similar to this, where an elevated slip road was being considered westbound, which would have taken airport-bound traffic over the roundabout and directly onto the Airport Hill. Needless to say, the cheap option won out

Good thinking though!

RubyXI

Anyone know what the story is for pedestrians?

sheff_

phi3 wrote: »

Anyone know what the story is for pedestrians?

Lots of traffic lights and waiting

Max_Charger

sheff_ wrote: »

Lots of traffic lights and waiting

Yup, if you're coming from Eagle Valley trying to get to Tesco, you've to go through 7 sets of pedestrian lights. 8 if you count the ones outside Tesco separately as there are 2 sections. Painful.

RubyXI

sheff_ wrote: »

Lots of traffic lights and waiting

I meant when it's done! I know, it's a disaster now.

sheff_

phi3 wrote: »

I meant when it's done! I know, it's a disaster now.

What's there now now is essentailly how it will be, as pointed out by Max Charger.

Superb planning for a residential area.

AugustusMinimus

I thought the original plans had a tunnel under the roundabout for pedestrians ?

So many traffic lights to traverse is not nice.