N40 - Cork South Ring Bandon & Sarsfield Flyovers

blindsider wrote: »

I'm sure 18 months was mentioned somewhere. Bonuses and penalties for on time completion will play a part also. They'll be doing a lot of night work as with the Kinsale Rd flyover.

Whatever about timeframes etc, it really is good to see this project started - it will make a big difference to local traffic. Hopefully Dunkettle can be sorted in the meantime also.

I think it should take a lot of traffic out of Bishopstown on top of free up both roundabouts and the SRR.

A lot of people go through Wilton and Bishopstown in order to avoid those two roundabouts. Travelling West out of Cork City centre, the Wilton road from Victoria Cross all the way to Sarsfields Road Roundabout is like a wall to traffic. Only 4 junctions that allow traffic through it. At least now one of those junctions will allow west-east traffic flow without traffic lights.

corktina wrote: »

how so? there may be a slight increase in traffic using that route but the overall volume will be much as now surely

Just say there is a 1/2 mile backup going east into the Sarsfields Roundabout. Remove the roundabout, and you will add this 1/2 of backed up traffic to the backup from the tunnel. If there is 1/2 mile at the Bandon roundabout and you are adding another half a mile to the tunnel backup.

This isn't a major problem in itself. However, if the backup comes up to the Kinsale Road Roundabout, it cause traffic chaos with traffic trying to merge into a backup. Another issue is if this cause the traffic going to the tunnel to be backed up past the Bloomfield interchange. This will directly affect traffic moving east attempting to leave the SRR via the Bloomfield Interchange. If there is no backup past this interchange, this traffic movement would not be affected.

In the end, if you take the South Ring Road alone, the two roundabout at present only break up the backed up traffic into bite size pieces. Remove them and you are adding it to the next backup. In the end, the total amount of cars backed up will be the same. They will just be backed up in a different place.

However, removing these two roundabouts will hugely benefit traffic going west and all other movements on the roundabouts.

However, this will piss me off no end. I use the tunnel but only ever join the SRR at Kinsale Roundabout. In essance, those joining the SRR after Sarsfield Roundabout will now also get their fill of the former backups at those roundabouts too. A motorway network is only as good as it's worst junction.

corktina wrote: »

thats a bit of a myth imho
The thing is that 1/2 mile tailback will also have got to the roundabout quicker and be long gone. If the overall traffic flow rate is about the same, then the tailback at Dunkettle will also still be the same speeding the overall journey for all.

That is simply not true.

Imagine two bags of sand, each with a hole in the bottom. One bag is on top of the other. The hole in the bottom of one is leaving sand in the top of the other.

If the hole are leaving the same volume of sand through, then the bag at the bottom will continue to contain the same volume of sand. However, if you double the volume of sand passing through the top bag, then the bottom bag will start to fill up as the sand simply can't get through the bottom one.

However, it will still take exactly the same about of time for both bags of sand to empty as the hole the bottom bag is the limiting factor for the entire system.

In the end, both the Sarsfield junction and the Dunkettle Interchange allow the same amount of traffic flow through them. You can only improve a traffic system be removing the worst junction. As the Dunkettle junction is just as bad as both Sarsfields and Bandon in terms of no of vehicles per hour, then the overall system is not being improved.

In fact, give that Dunkettle is an interchange of two national routes, I would imagine that Dunkettle as it expieriences even more traffic that Sarsfields or Bandon, then that it is indeed the weak link itself.

This is of course assuming that the majority of traffic travelling eastwards after Sarsfields will continue on the SRR.

Except that not everyone passing through the Sarsfield Road and Wilton roundabouts is heading towards Dunkettle.

corktina wrote: »

"if you double the volume of sand passing through the top bag" you arent doubling the volume, its jsut the same

In the end, the sand in the top bag will take exactly the same length of time to get through both bags. However, it will exit the top bag earlier and remain in the bottom bag for longer.

If this isn't true, it would mean more sand is getting through the bottom bag faster, eventhough the hole in the bottom bag is exactly the same size. Simply impossible.

I think the cue will become longer at the tunnel, I see what you are saying about the same volume of traffic, but cars will get to the tunnel quicker. They will be going through the tunnel at the same rate as now, so it makes sense that if cars are getting to the tunnel quicker and the flow through the tunnel stays at the same rate the cue will be longer, classic bottle neck.

Same argument for Newland's cross after the N7 upgrade as well I remember. The analogy with the bags of sand is useless as a road network is nothing like a single point of entry/exit system.

Gonna repeat my old post here:

http://www.boards.ie/vbulletin/showpost.php?p=65401331&postcount=62

One simple question I ask myself is "how many people drive from Ballincollig to Dunkettle at rush hour?"

The last roundabout before Dunkettle is at Sarsfield Rd. Is every car waiting at that roundabout going to go through the tunnel? There are 6 exits before the tunnel:
1) Togher
2) Turner's X, City Center (Link), Airport
3) Douglas (West)
4) Douglas (East)
5) Carrigaline, Rochestown
6) Mahon Point

An absolutely massive catchment of Cork's population who, if going home, will get off before the tunnel.

I agree there are times when dunkettle backs up really badly, and this can affect the link, and this might be made slightly worse by traffic rapidly approaching, but it'll be infrequent. It's certainly not enough to have an overall negative impact associated with building the flyovers.

How many 'bags of sand' will pour out at these intersections with major population areas? My guess is a lot. This is a pretty advanced queue system. Yes the arrival rate of cars to the tunnel will be less controlled, and at certain times there may be anomalies, but overall I think the effect on the system will be positive.

Start date 6th July! Whoop Whoop!

28th June 2011
Re: N25 Bandon/Sarsfield Interchanges Upgrade
Progress Update
Wednesday 6th July 2011 has now been established as the contract start date for the above scheme. Cork City Council
have appointed SIAC Construction Ltd. to carry out the works. Arup Consulting Engineers will act as Cork City
Council’s representatives for the Contract and RPS Ltd. will act as SIAC’s designer’s for the Scheme.
The Scheme comprises the upgrading of over 3km of the N25 South Ring Road including:
• Grade separation at Sarsfield Road Roundabout and Bandon Road Roundabout.
• Construction of a realigned dual carriageway along the new route.
• Construction of new parallel link roads between Sarsfield Road and Bandon Road.
• Demolition of existing pedestrian bridges at Sarsfield Road Roundabout and near Bandon Road Roundabout.
• New cycleways and footpaths.
• Installation of traffic signals, signage including gantry signs, public lighting, noise barriers, etc.
A scale model indicating the scope of works to be carried out as part of the scheme is on display in the foyer of County
Hall – this area is open to the public during normal office hours.
A two year construction period has been indicated giving an initial contract completion date of July 2013.
Preliminary works will be getting underway over the coming days. These will include survey works, identification and
location of existing services, establishment of site office, material deliveries to site etc. These preliminary works will
continue for a number of weeks and no disruption to traffic flow is anticipated during this period.
Preliminary works include the setting up of a project office on site. Contact details for this project office will be
circulated in due course. Also, a 24 hour freephone helpline will be established for the duration of the construction phase
– again contact details will be circulated in due course. Pending completion of the onsite office queries should be
channeled to the above telephone number or directly to site staff via the following mobile numbers:

AugustusMinimus wrote: »

Interesting design.

Am I right in saying, on exiting Sarsfields roundabout, travelling westwards, you will have to also negotiate the Bandon roundabout before getting onto the mainline South Ring Road ?

Looks to be the same when exiting the Bandon Roundabout travelling eastwards.

I noticed that aswell. If that is the case then there will still be tailbacks (although not as bad as the current situation) between Bandon and Sarsfield R'abouts.

AugustusMinimus wrote: »

Although, to access Sarsfields travelling westwards, you'll first have to go through the Bandon roundabout by the looks of things.

What do you mean? If travelling west you arrive at Sarsfield before Bandon and there is an off ramp for it.

Hogzy wrote: »

What do you mean? If travelling west you arrive at Sarsfield before Bandon and there is an off ramp for it.

Sorry. Should have said eastwards.

Appears to be no slip road when travelling eastwards directly onto the Sarsfields Roundabout. Have to go through Bandon first.