Third Menai Crossing (consultation)

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c2R
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Third Menai Crossing (consultation)

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Last edited by Steven on Thu Aug 11, 2016 08:45, edited 1 time in total.
Reason: Slight title edit
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Re: Third Meni Crossing (consultation)

Post by Bryn666 »

Given the A55 runs as dual carriageway right up to the bridge on both sides am I right in thinking a new bridge would be relatively close to the existing?

I'm surprised given the width of the bridge deck that it hasn't already been remarked as S4. Or at least 3 lane tidal flow.
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Re: Third Meni Crossing (consultation)

Post by rhyds »

Bryn666 wrote:Given the A55 runs as dual carriageway right up to the bridge on both sides am I right in thinking a new bridge would be relatively close to the existing?

I'm surprised given the width of the bridge deck that it hasn't already been remarked as S4. Or at least 3 lane tidal flow.
I think it would be a tight squeeze for S4 under the "arches" of the current bridge, and with junctions close to each end of the bridge tidal flow could be "challenging", however as you say it is odd that neither has been seriously considered for the 10+ years the bridge has been under capacity.

Is it possible the road deck isn't strong enough to carry 3/4 lanes?
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Re: Third Meni Crossing (consultation)

Post by wrinkly »

There was a previous consultation about this in November 2007. I don't know whether any WAG documents about it are still online. See this thread:

http://www.sabre-roads.org.uk/forum/vie ... =1&t=18838

Any new bridge would be immediately alongside the existing Britannia Bridge. I'm fairly sure the preferred option in the previous consultation was a new bridge on the east side, thus for mainland-bound traffic.

The present road deck is definitely not wide enough for S4, probably not even with lanes as narrow as those on the A1 at Gateshead where three lanes have been squeezed through spans only ever meant for two - and I'm sure lanes that narrow would not be allowed on a two-way carriageway.

My impression is that the present carriageway is about 10m through the arches, and it has no marginal strips:

https://www.google.co.uk/maps/@53.21594 ... 312!8i6656

Edit: This WG page says 9m:

http://gov.wales/topics/transport/roads ... e/?lang=en

The previous consultation dismissed tidal flow. I think it also said there's not a lot of spare strength in the structure, and for that reason dismissed widening the deck by demolishing the arches.

Further edit: Wikipedia has a bit about the 2007 consultation.

Yet further edit: see also "Update 7" at the bottom of this page.

I've also seen talk of restoring the rail deck to two tracks - currently one track and a narrow service/access road.
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Re: Third Meni Crossing (consultation)

Post by KeithW »

rhyds wrote:
I think it would be a tight squeeze for S4 under the "arches" of the current bridge, and with junctions close to each end of the bridge tidal flow could be "challenging", however as you say it is odd that neither has been seriously considered for the 10+ years the bridge has been under capacity.

Is it possible the road deck isn't strong enough to carry 3/4 lanes?
There is no way you could get 4 lanes over the current bridge, those gaps in the piers were designed to carry a railway and as I recall from the 2007 study the existing structure would not carry the weight especially given the growing size of cars and trucks. The existing bridge was a brilliant piece of lateral thinking when the old railway bridge tube section burned out but I don't think you could realistically stretch the original design much further. Any reuse would essentially require the complete closure and reconstruction of the bridge to road and rail traffic for several years with all the traffic having to use Telford's old road bridge which is completely incapable of handling current vehicle movements.
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Re: Third Menai Crossing (consultation)

Post by jackal »

It's puzzling that this hasn't been provided already given it's such an obvious bottleneck and, if previous estimates of £100-200m are accurate, a fraction of the cost of, say, the Queensferry Crossing.
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Re: Third Menai Crossing (consultation)

Post by Bryn666 »

I had forgotten about the towers.

9m is an extremely unfortunate carriageway width to do much with.

I suspect the cheapest, but not most pleasant visually, option is to build a second bridge alongside and reduce the existing bridge to 7.3m to accommodate cyclists etc.

Was anything planned prior to the fire? It must have saved a fortune at the time if there was!
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Re: Third Menai Crossing (consultation)

Post by jackal »

Bryn666 wrote:I suspect the cheapest, but not most pleasant visually, option is to build a second bridge alongside and reduce the existing bridge to 7.3m to accommodate cyclists etc.
According to the Wikipedia page linked by wrinkly above, the previous scheme considered options for either a multi-span concrete box or single-span cable-stayed bridge adjacent to the current bridge, with the box bridge cheaper and less visually intrusive but raising environmental issues due to the support pillars in the strait.
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Re: Third Menai Crossing (consultation)

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Bryn666 wrote:Was anything planned prior to the fire? It must have saved a fortune at the time if there was!
I've often wondered about that but never seen any proof that there was.
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Re: Third Menai Crossing (consultation)

Post by Jam35 »

I hope they go for a Newborough-Caernarfon type of route. Would be a lot more use for local traffic than a third bridge to Bangor.
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Re: Third Menai Crossing (consultation)

Post by Chris Bertram »

Jam35 wrote:I hope they go for a Newborough-Caernarfon type of route. Would be a lot more use for local traffic than a third bridge to Bangor.
B4419 used to cross the strait via a ferry from Caernarfon to the Tal-y-foel pier, roughly in that area. That's why there's the seemingly redundant bit of that road in Caernarfon town centre.
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Re: Third Menai Crossing (consultation)

Post by KeithW »

Bryn666 wrote:I had forgotten about the towers.

9m is an extremely unfortunate carriageway width to do much with.

I suspect the cheapest, but not most pleasant visually, option is to build a second bridge alongside and reduce the existing bridge to 7.3m to accommodate cyclists etc.

Was anything planned prior to the fire? It must have saved a fortune at the time if there was!
No while trains were running within 18 months it was almost 10 years before the road deck opened. There had been studies for a new bridge alongside the railway bridge but as I recall it was the County Surveyor who came up with the idea of rebuilding the damaged structure with a new road deck on top while preparing his report on the structure.
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Re: Third Menai Crossing (consultation)

Post by wrinkly »

KeithW wrote:
Bryn666 wrote:I had forgotten about the towers.

9m is an extremely unfortunate carriageway width to do much with.

I suspect the cheapest, but not most pleasant visually, option is to build a second bridge alongside and reduce the existing bridge to 7.3m to accommodate cyclists etc.

Was anything planned prior to the fire? It must have saved a fortune at the time if there was!
No while trains were running within 18 months it was almost 10 years before the road deck opened. There had been studies for a new bridge alongside the railway bridge but as I recall it was the County Surveyor who came up with the idea of rebuilding the damaged structure with a new road deck on top while preparing his report on the structure.
I hadn't heard of those studies before. It probably means that after the fire it was reasonably easy to adapt previous plans.

Draft orders for the road deck and Llanfairpwllgwyngyll bypass were published in Dec 1973, well under 4 years after the fire. Those for the Bangor bypass were a bit later.

I think reopening to trains was dependent on construction of the steel arch underneath, which was designed to carry the load of the road deck too.
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Re: Third Menai Crossing (consultation)

Post by KeithW »

wrinkly wrote:
KeithW wrote:
Bryn666 wrote:I had forgotten about the towers.

9m is an extremely unfortunate carriageway width to do much with.

I suspect the cheapest, but not most pleasant visually, option is to build a second bridge alongside and reduce the existing bridge to 7.3m to accommodate cyclists etc.

Was anything planned prior to the fire? It must have saved a fortune at the time if there was!
No while trains were running within 18 months it was almost 10 years before the road deck opened. There had been studies for a new bridge alongside the railway bridge but as I recall it was the County Surveyor who came up with the idea of rebuilding the damaged structure with a new road deck on top while preparing his report on the structure.
I hadn't heard of those studies before. It probably means that after the fire it was reasonably easy to adapt previous plans.

Draft orders for the road deck and Llanfairpwllgwyngyll bypass were published in Dec 1973, well under 4 years after the fire. Those for the Bangor bypass were a bit later.

I think reopening to trains was dependent on construction of the steel arch underneath, which was designed to carry the load of the road deck too.
There was no adaptation of previous plans as those involved a completely new and separate structure. The bridge was of course seen at the time as primarily a railway bridge and getting the boat trains to Holyhead running again was the number one priority. The arches were needed to support the train deck as the old tubes had been damaged beyond repair but its a tribute to the engineers that they didn't just take the easy option of replacing the tubes with a new structure of similar design using modern materials which would have undoubtedly been cheaper and easier. In fact work on the road bridge only started in 1977 but the new steel arch bridge had enough spare capacity built in to handle the load.

See http://www.engineering-timelines.com/sc ... sp?id=1415 for more details
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Re: Third Menai Crossing (consultation)

Post by Owain »

I've used the A55 on a number of occasions, and never found any problem with the Menai crossing. There are surely a great many stretches of road that need more urgent attention than this?
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Re: Third Menai Crossing (consultation)

Post by Big L »

Owain wrote:I've used the A55 on a number of occasions, and never found any problem with the Menai crossing. There are surely a great many stretches of road that need more urgent attention than this?
I can think of one on the A55, fun though it is creeping around those cliffs at 30.
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Re: Third Menai Crossing (consultation)

Post by rhyds »

Owain wrote:I've used the A55 on a number of occasions, and never found any problem with the Menai crossing. There are surely a great many stretches of road that need more urgent attention than this?
Outside of the morning and afternoon peaks its manageable, but during the peaks it is absolutely rammed because there are only two S2 connections between Bangor (the area's main employment centre and home to a substantial university) and Ynys Mon (where a lot of folk who work in Bangor live) and everyone's trying to get in to/out of town.

Also, despite the straights, places like Porthaethwy/Menai Bridge and Llanfairpwll are almost extensions of Bangor (even down to having 01248 phone numbers) so there's usually a steady rate of crossing traffic on both the Menai and Britannia bridges.

The other thing of course is that either side of the Britannia Bridge is grade separated D2 as far as Caergybi/Holyhead and the roundabouts at the A55 tunnels. Its basically North Wales' equivalent to the M4/A48 Britton Ferry bridge
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Re: Third Menai Crossing (consultation)

Post by rhyds »

Big L wrote:
Owain wrote:I've used the A55 on a number of occasions, and never found any problem with the Menai crossing. There are surely a great many stretches of road that need more urgent attention than this?
I can think of one on the A55, fun though it is creeping around those cliffs at 30.
IIRC the new tunnel was designed with space to bore a second route through to replace that section.
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Re: Third Menai Crossing (consultation)

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KeithW wrote:There was no adaptation of previous plans as those involved a completely new and separate structure.
Sorry I wasn't clear. The point I was trying to make there was that if any planning for the Bangor and Llanfairpwll bypasses was done before the fire on the assumption that a new road bridge would be built alongside the Britannia Bridge, then that would require little alteration following the decision to add a road deck to the Britannia Bridge instead, because the Menai crossing would be in almost the same place in the two cases.
The bridge was of course seen at the time as primarily a railway bridge and getting the boat trains to Holyhead running again was the number one priority. The arches were needed to support the train deck as the old tubes had been damaged beyond repair but its a tribute to the engineers that they didn't just take the easy option of replacing the tubes with a new structure of similar design using modern materials which would have undoubtedly been cheaper and easier. In fact work on the road bridge only started in 1977 but the new steel arch bridge had enough spare capacity built in to handle the load.
The date construction started on the road deck is of limited relevance. The date of interest is the date it was decided in principle to add a road deck. I think this was quite soon after the fire (which was May 1970). The decision was certainly substantially earlier than December 1973, because draft orders were published then. The fact that the arches were strong enough to support a road deck as well as the rail deck was not just a happy accident as you suggest. I believe the decision in principle to add a road deck preceded the design of the arches.
On a quick scan that doesn't give any new information on the date of the decision in principle to add a road deck.

Edit: I now think the decision was announced in September 1970. I'll add more later.
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Re: Third Menai Crossing (consultation)

Post by wrinkly »

wrinkly wrote:The date of interest is the date it was decided in principle to add a road deck. I think this was quite soon after the fire (which was May 1970).

...

Edit: I now think the decision was announced in September 1970. I'll add more later.
I remember that I first read of the decision to add a road deck to the rail bridge in an article in the Guardian. The Guardian (and the Observer) have an online archive:

http://pqasb.pqarchiver.com/guardian/ad ... earch.html

To read articles in it costs money, but you can search it free of charge and read the titles of the articles found. Searching for "Menai" from May 1970 to Dec 1973 finds 55 hits, one of which is "Dual bridge for Menai", September 16, 1970.

The first train over the bridge after the fire was at the beginning of 1972 but I think one tube was still in place then. I'm not sure what date the rail deck was finished in its present form.
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