N21 - Abbeyfeale [route options published]

marno21

Kudos to @pajoguy for posting on the M21 thread

• 100m corridors to be revealed in Nov/Dec 2023
• ABP in summer 2024
• Assuming two years at ABP and a decision in mid 2026, and no judicial review, construction to start in 2028
• Completed by summer 2031

https://www.limerickleader.ie/news/home/1320146/houses-knocked-and-eighty-farmers-affected-for-limerick-bypasses.html

lordleitrim

https://www.radiokerry.ie/news/updates-expected-in-new-year-on-newcastle-west-and-abbeyfeale-bypasses-362664

Same article as pertains to Newcastlewest bypass.

pajoguy

https://www.limerick.ie/council/newsroom/news/n21-newcastle-west-n21-abbeyfeale-road-scheme-design-update-of-the-preferred

marno21

Looks like they're planning on a N21/R576 roundabout with the new road, old road, R576 and Feale Bridge N21 at Fealesbridge. Big safety improvement given the right turning traffic from the R576 to the N21 northbound having to turn across high speed traffic from Castleisland.

Raoul Duke

https://www.boards.ie/discussion/comment/121832062#Comment_121832062

Where does it show the future roundabout?

Cookiemunster

A design update for these schemes was published today, 27th March 2025.

This design update shows the proposed mainlines, side road realignments and junction layouts as well as whether the roads are in cut or on fill. Additionally, it shows the proposed access arrangements, indicative land take lines, watercourse diversions and the location of drainage ponds and other details.

https://www.n21abbeyfeale.ie/design-update-drawings

It looks like 2+2

MICKEYG

https://www.boards.ie/discussion/comment/123304036#Comment_123304036

Roundabouts. Aargh!

KrisW1001

https://www.boards.ie/discussion/comment/123305886#Comment_123305886

This is the size of roundabout used on 2+2 roads:

Castlebar Bypass - Google Maps

That’s 80 metres in diameter. If you can’t navigate a roundabout as big as the ones on this scheme, I don’t know what to say to you.

MICKEYG

https://www.boards.ie/discussion/comment/123305913#Comment_123305913

What made you think I can't navigate a roundabout?

It's having to slow down at the end of one section of 2x2 and then start going again on a new section of 2x2. We have the same setup on the Castleisland bypass. It's not the end of the world but not ideal.

I have the same "issue" re having to slow down for toll booths when the M50 has shown it can be all automated.

The less stops and starts the better the experience.

DumbBrunette

https://www.boards.ie/discussion/comment/123306175#Comment_123306175

It looks like the roundabouts are only at either end of the scheme, which is TII's preference when there is a change in road type. Hopefully if the rest of the N21 is upgraded to 2+2 then these roundabouts will be upgraded to GSJs.

KrisW1001

https://www.boards.ie/discussion/comment/123306175#Comment_123306175

This isn’t a busy enough stretch of road to justify a grade-separated junction on capacity grounds, so let’s look at the options open to the designers for that stretch of road: take the 80 m wide roundabout and the 100 m of road either side…

Option I: Let’s not delay Mickey under any circumstances; he’s a busy man you know.
Cost: €20 million for compact Grade-separated Junction

1. Travel 280 m in a straight line at 100 km/h : 10.1 seconds.

TOTAL: 10.1 s.

Option II: The crippling injustice of a roundabout
Cost: €1 million.

1. Slow from 100 to 40 km/h on approach over 100 m. Average speed of 70 km/h = 5 s
2. Traverse half the roundabout at 40 km/h: 125.6 m (per Junior Cert Maths) / 11 m/s. = 11.3 s.
3. Accelerate from 40 to 100 km/h on exit over 100 m at average 70 km/h = 5 s

TOTAL: 21.3 s.

Using the roundabout is all of 11.3 s slower. I think you’ll live.

MICKEYG

https://www.boards.ie/discussion/comment/123306291#Comment_123306291

It is not just about me, but of course you know that.

I think build it right the first time is always the cheapest option. If there are no plans to ever go back to it then fine but if we end up upgrading the junctions in 5-10 years it will cost double.

It will be a huge upgrade regardless.

Charles Babbage

https://www.boards.ie/discussion/comment/123306291#Comment_123306291

However a roundabout is significantly more dangerous, so there is a probability that someone will not live.

KrisW1001

https://www.boards.ie/discussion/comment/123306435#Comment_123306435

Er, no. The alternative to a roundabout isn’t no junction, it’s a compact GSJ. That has its own safety issues. No road is completely safe.

Taking the worst case of a lethally inattentive driver joining just as a car is to their immediate right, the roundabout is actually safer because of the lower speed. The “victim” car has longer to react, and their speed of impact will be much slower in any case.

Typical speed through a roundabout is around 40 km/h. The worst case of a car entering a roundabout without looking will be hit by another car at around 40-50 km/h. Fatality from car-to-car collisions at that speed is extremely unlikely, even for “T-bone” impacts like this.

Meanwhile, someone ignoring the stop-line on a GSJ on-road and entering without looking will be hit by a car travelling at 100 km/h. At that speed, side-impacts have a very high chance of being fatal.

@MICKEYG - I’m mostly in agreement with you - it will be a great improvement, and I hope you didn’t take my example as anything more than good-natured ribbing. The point I was making is that, while it’d be great to allow the fastest possible travel, it comes at a very high cost for very little actual benefit.
The only reason to use a compact GSJ is when most traffic is through-traffic and there’s a lot of traffic overall. At lower traffic levels, and wherethe traffic is more evenly split between joining and through traffic, a roundabout is more efficient.

spacetweek

When you consider how many other very busy and much higher traffic junctions are in other parts of the country, if this scheme is done with roundabouts there is no chance of them coming back later and replacing them with GSJ’s. In this case, roundabouts are totally justified as a design choice.