Why are the M7/M9 and M7/M8 junctions restricted??

Chris_533976

I've long wondered this. The current M7/M9 and the in construction M7/M8 junctions are restricted and I want to know why.

If you're coming northbound on the M9, you end up going towards Dublin - theres no sliproad to take you in the Limerick direction. Similarly, on the future M8, traveling from the Cork direction you wont be able to turn towards the Limerick direction. Again, theres a simple slip road missing.

What bugs me is that in both these junctions, the missing movements would be easy to add. Why aren't they there? Whether traffic levels warrant it directly or not, it seems silly not to have them. Why aren't they there?

murphaph

Chris_533976 wrote:

I've long wondered this. The current M7/M9 and the in construction M7/M8 junctions are restricted and I want to know why.

If you're coming northbound on the M9, you end up going towards Dublin - theres no sliproad to take you in the Limerick direction. Similarly, on the future M8, traveling from the Cork direction you wont be able to turn towards the Limerick direction. Again, theres a simple slip road missing.

What bugs me is that in both these junctions, the missing movements would be easy to add. Why aren't they there? Whether traffic levels warrant it directly or not, it seems silly not to have them. Why aren't they there?

Correction chris, one of the missing movements would be relatively easy to add. The M7(N) -> M9(S) movement (for example) would not be so easy and would require bridges or tunnels.

I agree though that the easy fix slip should be considered at both these junctions.


Edit: Sorry. I see you just meant the simple movements in the first place!

Victor

There are alternative routes available to make those movements. In any case, doing those movements is taking two sides of a triangle.

I think the term is "limited" or "partial", not "restricted".

Zoney

All roads go to Dublin?

Rovi

A cynical person might suggest that the M7/M8 one is restricted so as to force everyone to go through the toll plaza to the north of it...

icdg

In the case of the M7/M9 junction, cost! This was 1993 - when all our sections of motorway in the country put together were much shorter than the M1 alone is now. And yes, the "all roads lead to Dublin" mindset was probably in the designers heads - and may still partially be in the heads of the designers of the M7/M8 junction, although there's less to understand there. Incidently, the M4/M6 (and it is M6 at this particular point, despite what some of the signs say) is exactly the same.

Incidently, what was then M7 J9 (now J11) was the first motorway-motorway interchange ever built in this country. Strange how fifteen years later, we still have not managed to build a fully-free flowing motorway-motorway interchange which allows all movements - the three above and the M11-M50 junctions are all restricted and the M1/M50 junction, the only full access one, has traffic lights (under motorway regulations!).

Chris_533976

The closest we'll get I guess is the (presumably M's eventually) M6/M18/M17 interchange near Galway. That'll be a three level stack.... M6 East-West on the bottom, then a roundabout above, then above that the M17/M18.

Wont be freeflow, but all movements will be as free as possible. I'm not 100% convinced that its the best design, but I dont think traffic levels would warrent full freeflow.

icdg

If the N6 is reclassified motorway prior to opening (as seems to be the Government's intention), and there is no other public acccess to this junction, then yes, the N18 and N17 from this junction until their next exits will become motorways, as any road leading inescapably to a motorway must also be a motorway. Hence why the N6 becomes M6 for a short section eastbound from Junction 2, until it meets the M4. Traffic can't go anywhere else from there (and indeed, is stuck on the M4 all the way to Enfield!).

murphaph

icdg wrote:

If the N6 is reclassified motorway prior to opening (as seems to be the Government's intention), and there is no other public acccess to this junction, then yes, the N18 and N17 from this junction until their next exits will become motorways, as any road leading inescapably to a motorway must also be a motorway. Hence why the N6 becomes M6 for a short section eastbound from Junction 2, until it meets the M4. Traffic can't go anywhere else from there (and indeed, is stuck on the M4 all the way to Enfield!).

That's not guaranteed as a 3 level stack allows u-turning or indeed you could travel N18<->N17 without touching the N6. Of course, the N18/N17 my be m-ways in their own right.

Chris_533976

I think they will be M.

JupiterKid

In terms of the current motorway to motorway junctions, the current simple forks of the M7/M9 and M4/M6 interchanges work perfectly fine. There is little demand to travel in the movements not possible in these junctions.

I think that in the next decade, there will however be a demand for motorway to motorway junctions that will have free flowing movements in all directions. But using a three level stack with roundabout in the middle is a terrible idea, the CBRD website gives plenty of reasons not to adopt this junction design which is considers to be cheap n' nasty. This is also not the type of junctions being rebuilt along the M50. I think that the Whirlpool, Partially unrolled cloverleaf (a la M50) or the four level stack are the way to go.

Check out this link:
http://www.cbrd.co.uk/reference/interchanges/

Victor

For the N6/N17-18 I don't really see a huge number of right turning movements - I suspect Tuam-Galway and Galway-Limerick would be the main ones.

Three-Level Stacked Roundabout with left-turn lanes bypassing the roundabout, is slightly better than vanilla Three-Level Stacked Roundabout.

murphaph

JupiterKid wrote:

In terms of the current motorway to motorway junctions, the current simple forks of the M7/M9 and M4/M6 interchanges work perfectly fine. There is little demand to travel in the movements not possible in these junctions.

I think that in the next decade, there will however be a demand for motorway to motorway junctions that will have free flowing movements in all directions. But using a three level stack with roundabout in the middle is a terrible idea, the CBRD website gives plenty of reasons not to adopt this junction design which is considers to be cheap n' nasty. This is also not the type of junctions being rebuilt along the M50. I think that the Whirlpool, Partially unrolled cloverleaf (a la M50) or the four level stack are the way to go.

Check out this link:
http://www.cbrd.co.uk/reference/interchanges/

I'd go along with that. The land cost should be relatively low. What does agricultural land in rural county Galway run to? The 3 level stack is one of the most awkward junctions to upgrade to fully freeflowing and while I believe it will be sufficient for a few years, long term there will be hold ups at this junction, particularly the M18(N)->M6(E) movement and probably the M17(S)->M6(W) in the mornings.

Zoney

murphaph wrote:

The 3 level stack is one of the most awkward junctions to upgrade to fully freeflowing and while I believe it will be sufficient for a few years, long term there will be hold ups at this junction, particularly the M18(N)->M6(E) movement and probably the M17(S)->M6(W) in the mornings.

Galway to Limerick and Tuam to Galway will both require a travel via the roundabout and they are conflicting movements with heavy traffic.

The N6-N17-N18 junction should have been a custom interchange layout facilitating freeflow straight through on N6, from N6E to N17 and N18, and vice-versa N17/N18 to N6E. The other movements are less important - N17-N18 both directions, N17 to N6W, N18 to N6W and N6W to N17/N18.

Three level stack facilitates N17-N18 which isn't an essential movement - most people using the junction and N17 or N18 are going to/from Galway.

Chris_533976

CRBD overestimates how difficult these things are to upgrade. In an urban area, its nigh on impossible, but you can easily add slips and bridges here because its in the middle of nowhere.

That said, a better junction would be appreciated.

RadioCity

It's a while since I was in Sligo, but will the M4 technically begin there?
Is that bit of dual carriageway totally grade separated?

spacetweek

RadioCity wrote:

It's a while since I was in Sligo, but will the M4 technically begin there?
Is that bit of dual carriageway totally grade separated?

It is but I think you'd be stretching it to call it a motorway, it is grade separated but the design standard doesn't look great especially at this junction.

Felmwood

Recently when traveling south from Dublin to Cork I overshot the M8 junction on the M7 near Portlaoise, haveing travelled that road on a number of occassions I felt utterly stupid for doing so, but following conversations with several other people (of all ages) I discovered that they all had made the same mistake. All agreed that it is the poor lay out and markings of the split of two major morways (M7 and M8) that contribute to people making this mistake. In order to get back on track8 one has to travel several miles cross country to join the M8. I am just wondering are there many others who have missed the M8 junction of the M7.

namloc1980

Felmwood wrote: »

Recently when traveling south from Dublin to Cork I overshot the M8 junction on the M7 near Portlaoise, haveing travelled that road on a number of occassions I felt utterly stupid for doing so, but following conversations with several other people (of all ages) I discovered that they all had made the same mistake. All agreed that it is the poor lay out and markings of the split of two major morways (M7 and M8) that contribute to people making this mistake. In order to get back on track8 one has to travel several miles cross country to join the M8. I am just wondering are there many others who have missed the M8 junction of the M7.

Never missed it but I agree that it's a crap junction. More like a regular junction exit than a major motorway intersection.

L1011

M7/M9 due to when it was built. Wasn't any intention to extend the M9 at the time so little need was seen.

M7/M8 due to not wanting to let people use that bit of road toll-free... ditto why there's missing junction numbers for future use.

parsi

Something similar happens when coming into Limerick from Cork - left to the tunnel and right to the Dublin road. A straight-ahead to the City would be nice.

corktina

suddenly im 4 years younger again...

Victor

namloc1980 wrote: »

Never missed it but I agree that it's a crap junction. More like a regular junction exit than a major motorway intersection.

Meh.

It is the interchange immediately after the toll. Perhaps they should add a "I forgot my turn-off lane".

Chris_5339762

MYOB wrote: »

M7/M8 due to not wanting to let people use that bit of road toll-free... ditto why there's missing junction numbers for future use.

The missing junctions on the M7 and 8 were originally standard junctions but were deemed by An Bord Pleanala to be too close to the M7/8 split just in case it got all movements added. So they said that it wasnt worth refusing the whole scheme, but was worth removing those junctions so that all movements could be added if necessary.

highlydebased

parsi wrote: »

Something similar happens when coming into Limerick from Cork - left to the tunnel and right to the Dublin road. A straight-ahead to the City would be nice.

Indeed- it used always be straight ahead for city centre! But taking N18 and dock road exit is just as quick to city centre, Childers Road traffic can be quite bad at times.

Chris_5339762

..and thats exactly why they removed it. They didnt want Childers Road traffic backing up onto the M20 mainline.