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N5 - Westport to Turlough [open to traffic]

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  • Registered Users Posts: 4,680 ✭✭✭serfboard


    This junction was always planned to be a roundabout.
    Don't disagree that it was always planned to be roundabout.
    The amount of traffic going on/off the DC to access Castlebar is too high for a GSJ.
    What? There are GSJs on the M50 for God's sake. Is somebody seriously saying that there is going to be more traffic around Castlebar than there is on the M50?

    This smacks to me of making an argument to suit an outcome that was already wanted.


  • Registered Users Posts: 1,494 ✭✭✭KrisW1001


    The M50 carries about five times the traffic that this road does, so it needs full GSJs.

    The junction types on this road are compact Grade-separated Junctions - they have much shorter on- and off- ramps, and that limits the amount of space dedicated to leaving and joining traffic on the mainline. They are grade-separated primarily to prevent right-turners blocking or conflicting with through-traffic. They're used where most of the movement is along the main road, with only small amount of traffic joining and leaving.

    On the other hand, where the movements are evenly split between traffic staying on the road and traffic joining and leaving, then a large roundabout is a better use of the land and funds, and will make traffic flow better. That reason is stated in the text DumbBrunette posted. It's not an after-the-fact argument; it's sound engineering.

    Just because it was wrong to put roundabouts on high-traffic roads, it does not mean it's wrong to use them on a scheme like this with less than 20k AADT. A full motorway/motorway junction would certainly improve traffic flow at these points (maybe shaving a whole 30 seconds off transit times through the junction), but it would do so at 5-10 times the cost of a roundabout while using much more land.


  • Registered Users Posts: 999 ✭✭✭riddlinrussell


    KrisW1001 wrote: »
    The M50 carries about five times the traffic that this road does, so it needs full GSJs.

    The junction types on this road are compact Grade-separated Junctions - they have much shorter on- and off- ramps, and that limits the amount of space dedicated to leaving and joining traffic on the mainline. They are grade-separated primarily to prevent right-turners blocking or conflicting with through-traffic. They're used where most of the movement is along the main road, with only small amount of traffic joining and leaving.

    On the other hand, where the movements are evenly split between traffic staying on the road and traffic joining and leaving, then a large roundabout is a better use of the land and funds, and will make traffic flow better. That reason is stated in the text DumbBrunette posted. It's not an after-the-fact argument; it's sound engineering.

    Just because it was wrong to put roundabouts on high-traffic roads, it does not mean it's wrong to use them on a scheme like this with less than 20k AADT. A full motorway/motorway junction would certainly improve traffic flow at these points (maybe shaving a whole 30 seconds off transit times through the junction), but it would do so at 5-10 times the cost of a roundabout while using much more land.

    Great points, a Compact GSJ is not 'The same as a GSJ, just smaller', capacity is impacted by the space provided for exiting the mainline, the junctions created on the over/underbridge etc


  • Registered Users Posts: 782 ✭✭✭DumbBrunette


    Took a walk on the Greenway today past the works on the N59 north of Westport. Pic here of the cutting being dug through Barleyhill to bypass the notorious bends at that location. The cutting will come down to approximately the level of the existing road, and an embankment will be built up in the foreground to meet it.

    553541.jpg


  • Registered Users Posts: 374 ✭✭Reuben1210


    KrisW1001 wrote: »
    The M50 carries about five times the traffic that this road does, so it needs full GSJs.

    The junction types on this road are compact Grade-separated Junctions - they have much shorter on- and off- ramps, and that limits the amount of space dedicated to leaving and joining traffic on the mainline. They are grade-separated primarily to prevent right-turners blocking or conflicting with through-traffic. They're used where most of the movement is along the main road, with only small amount of traffic joining and leaving.

    On the other hand, where the movements are evenly split between traffic staying on the road and traffic joining and leaving, then a large roundabout is a better use of the land and funds, and will make traffic flow better. That reason is stated in the text DumbBrunette posted. It's not an after-the-fact argument; it's sound engineering.

    Just because it was wrong to put roundabouts on high-traffic roads, it does not mean it's wrong to use them on a scheme like this with less than 20k AADT. A full motorway/motorway junction would certainly improve traffic flow at these points (maybe shaving a whole 30 seconds off transit times through the junction), but it would do so at 5-10 times the cost of a roundabout while using much more land.

    Thanks for this - Is there an argument at all in the context of this road that GSJ should be used instead of roundabouts to 'future proof' the road in the case of large economic activity and population increases in years to come?


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  • Registered Users Posts: 782 ✭✭✭DumbBrunette


    Compact GSJs wouldn't achieve that, as they actually have a lower capacity than the 80 metre diameter roundabouts being used at Castlebar west and some of the other at grade junctions.

    Of course, you could make an argument for motorway style freeflow junctions to be provided, but per the TII standards these are not supposed to be used on Type 2 DCs, and as stated above, they would be relatively expensive.
    Reuben1210 wrote: »
    Thanks for this - Is there an argument at all in the context of this road that GSJ should be used instead of roundabouts to 'future proof' the road in the case of large economic activity and population increases in years to come?


  • Registered Users Posts: 374 ✭✭Reuben1210


    Sorry I maybe misunderstood the difference between a free-flow and a GSJ?


  • Registered Users Posts: 782 ✭✭✭DumbBrunette


    Not all GSJs are necessarily freeflow, for example the compact GSJs to be used on this scheme are similar to those at Claremorris, Knock and Charlestown, all of which have stop signs for traffic joining the mainline.

    The old M50 junctions (prior to the upgrade 10 years ago) were also grade separated, but they weren't freeflow as traffic had to stop for roundabouts and traffic lights.
    Reuben1210 wrote: »
    Sorry I maybe misunderstood the difference between a free-flow and a GSJ?


  • Registered Users Posts: 6,813 ✭✭✭Pete_Cavan


    I get the idea behind having a roundabouts at gateways into the major towns where "heavier turning movement flows are likely". What I dont get is why Castlebar west is considered to be the junction which requires the roundabout. Traffic coming from east or south of the town, likely to be the vast majority of the traffic, is going to use one of the other junctions. It is only really traffic coming from Westport which would use that western junction, and even then some of that will continue round to use one of the other junctions if travelling to the centre or eastern side of Castlebar.


  • Registered Users Posts: 5,550 ✭✭✭veryangryman


    Tullamore bypass is the perfect example of why roundabout junctions should be a nono for any road that goes anywhere near a large town. Can't ever get a straight run at it without being backed up on at least 2 of the roundabouts at any time of the day


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  • Registered Users Posts: 1,494 ✭✭✭KrisW1001


    The roundabouts on N5 are 80 m diameter, the Tullamore bypass roundabouts are only 40 m in size, with the exception of the large one at the northern end.


  • Registered Users Posts: 782 ✭✭✭DumbBrunette


    If you look at the traffic counter data, the busiest approach roads to Castlebar at the moment are N5 east, N5 west, N60 and N84, in that order, so the two busiest roads are getting roundabouts while the other two national roads aren't (which is at least logical).

    The key difference between the Castlebar west junction and the N60 and N84 junctions is the amount of traffic expected to enter and leave the dual carriageway. The N60 and N84 are very busy but most traffic is expected to be heading straight in/out of Castlebar, not turning on/off the DC.

    At Castlebar west, 3,000 vehicles a day travelling between Castlebar town centre and Westport are expected to enter and leave the DC at this junction (see below) which per the TII standards would be a very high flow for a compact GSJ, hence they opted for a roundabout. The design report states that a GSJ was considered but rejected on the basis that a roundabout would be better for traffic flow.

    553649.jpg
    Pete_Cavan wrote: »
    I get the idea behind having a roundabouts at gateways into the major towns where "heavier turning movement flows are likely". What I dont get is why Castlebar west is considered to be the junction which requires the roundabout. Traffic coming from east or south of the town, likely to be the vast majority of the traffic, is going to use one of the other junctions. It is only really traffic coming from Westport which would use that western junction, and even then some of that will continue round to use one of the other junctions if travelling to the centre or eastern side of Castlebar.


  • Registered Users Posts: 6,813 ✭✭✭Pete_Cavan


    If you look at the traffic counter data, the busiest approach roads to Castlebar at the moment are N5 east, N5 west, N60 and N84, in that order, so the two busiest roads are getting roundabouts while the other two national roads aren't (which is at least logical).

    The key difference between the Castlebar west junction and the N60 and N84 junctions is the amount of traffic expected to enter and leave the dual carriageway. The N60 and N84 are very busy but most traffic is expected to be heading straight in/out of Castlebar, not turning on/off the DC.

    At Castlebar west, 3,000 vehicles a day travelling between Castlebar town centre and Westport are expected to enter and leave the DC at this junction (see below) which per the TII standards would be a very high flow for a compact GSJ, hence they opted for a roundabout. The design report states that a GSJ was considered but rejected on the basis that a roundabout would be better for traffic flow.

    Of course the National Primary route sees the most traffic, and at present all that traffic has to continue through the town as there is no suitable route around it. Everyone coming from Westport or adjacent areas going to anywhere in Castlebar has to do so via N5 west, there's no other option. When the bypass is in place, much of that traffic will likely continue around the bypass and use one of the other junctions. Looking at the layout of the town and the locations of the junctions, its hard to see how N5 west will continue to see as much traffic. Using it to access Castlebar would have you driving on poorer quality roads for longer, and having to pass through the town to get to anywhere that isn't the west side of the town. Most of the employment and large retail in Castlebar is on the eastern side of the town, much easier accessed from the N60 junction. Any point in the town centre is going to be 1.5km further from the new N5 west roundabout, than from the N84 junction.


  • Registered Users Posts: 4,018 ✭✭✭Cosmo Kramer


    I'd be really surprised if many people travelling into Castlebar town centre from the west decided to go around to the N84 junction to access the town. If you know the layout of the town then it doesn't make sense - if you go in via the old N5 from Westport you have very easy access to the town centre, the newer shopping area around Tesco and Dunnes, as well as the hospital and GMIT.

    Whereas if you go around to the Ballinrobe Road access you'll then have to wind your way in through Saleen, past the railway station, Spencer Park, Spencer Street and then around the Mall to get into the town - that route also includes two sets of lights compared to none on the current route. Next to nobody is going to choose to go that way.

    Some will go for the Breaffy Road access to get to that end of town, the industrial parks, out of town retail and McHale Park on match days, but the vast majority will come off at Derrylea and just go in the old road because it's the easiest way in.


  • Registered Users Posts: 4,680 ✭✭✭serfboard


    At Castlebar west, 3,000 vehicles a day travelling between Castlebar town centre and Westport are expected to enter and leave the DC at this junction (see below) which per the TII standards would be a very high flow for a compact GSJ, hence they opted for a roundabout. The design report states that a GSJ was considered but rejected on the basis that a roundabout would be better for traffic flow.
    Let's think about the traffic movements. What is the probability that someone travelling West on the N5 will access Castlebar from the Castlebar West junction? Zero, or vanishingly small.

    Equally, what is the likelihood that someone from the Western side of Castlebar, will use the Castlebar West junction to travel East? Again, zero or vanishingly small.

    Therefore, the only two movements needed are Eastbound traffic on the DC heading into Castlebar, and Castlebar traffic heading Westbound. The former simply needs a slip lane.

    The latter needs a bridge and a slip, which I accept is more expensive, but not compared to the two junctions that are being built at the N84 & N60. This, in my view, would constitute doing it properly.

    As I said before, I've no issue with the roundabouts at Castlebar East and Westport East, but forcing traffic to come to a complete stop in the middle of a dual carriageway is ridiculous, unnecessary and a less-safe approach then the one outlined above.

    There are logical arguments given as to why a roundabout was better, but should some form of GSJ have been chosen, there are plenty of logical arguments that could be wheeled out in favour of that approach. As I said, the end result is something that has all the hallmarks of a political decision, but which seeks to back up that political decision with engineering or logical arguments.

    And if anyone here thinks that businesses in Castlebar did not lobby to get a roundabout put in here, then that would make Castlebar one of the few (only) towns in Ireland that didn't. And remember, at the time that this was being designed, Castlebar had the most powerful politician in the country as their local TD.


  • Registered Users Posts: 1,494 ✭✭✭KrisW1001


    serfboard wrote: »
    As I said before, I've no issue with the roundabouts at Castlebar East and Westport East, but forcing traffic to come to a complete stop in the middle of a dual carriageway is ridiculous, unnecessary and a less-safe approach then the one outlined above.
    Roundabouts do not require traffic to come to a complete stop.

    What's more, the roundabout is achieving the very thing you are asking for: it evens up the priority of traffic flows such that traffic leaving Castlebar and wishing to head West is not starved of access by traffic on the mainline (Eastbound traffic is not an issue regardless of junction type, as it's a simple sliproad in either case).

    The only type of GSJ that would be allowed under the project budget would require joining traffic to yield to drivers already on the mainline, but at this point, there's actually as much traffic joining the mainline as going through it. A full free-flow GSJ with long merging lanes would be prohibitive in terms of land take and costs.

    But really: go back and look at those traffic counts that DumbBrunette posted: we are not talking about a busy motorway interchange here - it's a moderately trafficked rural road. The 2+2 road type is already far above the capacity needed, and has been chosen primarily for safety reasons. The roundabout is not going to delay you.

    Speaking personally, I would want to fire any transport authority that would approve an extra twenty million euro just so a few drivers can get through a quiet junction 30 seconds faster, and anything better than this roundabout would cost at least that.


  • Registered Users Posts: 2,464 ✭✭✭mayo.mick


    Some dashcam from yesterday on the N5 junction.



  • Registered Users Posts: 782 ✭✭✭DumbBrunette


    Embankment for the bridge over the Lodge Road in Westport, looking east toward the future Knockranny North roundabout. This area is very boggy and a lot of rock went in before the embankment started. Still a few more meters to go before it's topped out.

    553777.jpg


  • Registered Users Posts: 9,414 ✭✭✭irishgeo


    Embankment for the bridge over the Lodge Road in Westport, looking east toward the future Knockranny North roundabout. This area is very boggy and a lot of rock went in before the embankment started. Still a few more meters to go before it's topped out.

    553777.jpg

    What the plan for the great western Greenway in this area?


  • Registered Users Posts: 782 ✭✭✭DumbBrunette


    ABP actually required Mayo Co Co to make some significant changes to their original plans in order to better facilitate the Greenway and bicycle traffic in general in this area, including a fully grade separated crossing of the Westport relief road.

    553820.jpg
    irishgeo wrote: »
    What the plan for the great western Greenway in this area?


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  • Registered Users Posts: 782 ✭✭✭DumbBrunette


    Great aerial shot of the works to bypass the bends at Barleyhill on the N59. The Great Western Greenway runs through the trees in the foreground.

    553851.jpg

    Pic courtesy of Jack Walsh drone photography.


  • Registered Users Posts: 5,868 ✭✭✭Chris_5339762


    Those really are some terrible bends. Fair play to whoever in authority insisted on bundling them with this scheme


  • Registered Users Posts: 4,018 ✭✭✭Cosmo Kramer


    Michael Ring would be my guess there.


  • Posts: 0 [Deleted User]


    Where will Newport-Westport traffic go while they're building this stretch of road? Will the N59 along this road be closed completely and traffic diverted to the Newport-Castlebar Road?


  • Registered Users Posts: 18,517 ✭✭✭✭kippy


    Where will Newport-Westport traffic go while they're building this stretch of road? Will the N59 along this road be closed completely and traffic diverted to the Newport-Castlebar Road?

    They can build most of the new road without impacting existing. May need to be closed (small diversion to the right across a new part) while it is finished.
    I don't think it's a big deal tbh


  • Registered Users Posts: 782 ✭✭✭DumbBrunette


    New aerial shot showing the realigned N59, the N5/N59 roundabout and the Westport relief road stretching into the distance.

    553971.jpg

    Link: https://m.facebook.com/photo.php?fbid=2916224038704968&id=2224058757921503&set=pcb.2916224135371625&source=49&refid=13&__tn__=%2B%3D


  • Moderators, Science, Health & Environment Moderators Posts: 4,992 Mod ✭✭✭✭spacetweek


    ABP actually required Mayo Co Co to make some significant changes to their original plans in order to better facilitate the Greenway and bicycle traffic in general in this area, including a fully grade separated crossing of the Westport relief road.
    It’s not yet clear to me how the GWG will end up but I hope the above changes eliminate the very steep hill at the start of the greenway north of Westport. This hill forces cyclists to dismount and walk their bikes up the hill and should not have been part of the design. A grade change is unavoidable but it must be done gently.


  • Registered Users Posts: 41 thomas385


    spacetweek wrote: »
    It’s not yet clear to me how the GWG will end up but I hope the above changes eliminate the very steep hill at the start of the greenway north of Westport. This hill forces cyclists to dismount and walk their bikes up the hill and should not have been part of the design. A grade change is unavoidable but it must be done gently.

    As far as I can remember from the plans, that steep hill will become an access road from the Allergan roundabout to the houses on the hill. The Greenway will be rerouted, so as you follow the road down the Allergan Road, where previously you had to go up the steep hill, you will now continue flat along by one of the old railway gate houses, behind the back of the GAA pitch, under the new road, and then conencting with the Greenway as present.


  • Registered Users Posts: 483 ✭✭elchupanebrey


    thomas385 wrote: »
    As far as I can remember from the plans, that steep hill will become an access road from the Allergan roundabout to the houses on the hill. The Greenway will be rerouted, so as you follow the road down the Allergan Road, where previously you had to go up the steep hill, you will now continue flat along by one of the old railway gate houses, behind the back of the GAA pitch, under the new road, and then conencting with the Greenway as present.

    That steep hill part of the greenaway is now closed until the project is completed as far as I know, so the alternative access to the greenway, via the Newport rd will have to be used in the mean time.


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  • Registered Users Posts: 782 ✭✭✭DumbBrunette




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