Tunnels or Bridges

veryangryman

Ive always wondered what dictates whether to build a tunnel over a bridge for river/lake crossings.

Is there any reason for instance why Shannon Tunnel (and not bridge) considered. Or the Lee Tunnel?

dubhthach

veryangryman wrote: »

Ive always wondered what dictates whether to build a tunnel over a bridge for river/lake crossings.

Is there any reason for instance why Shannon Tunnel (and not bridge) considered. Or the Lee Tunnel?

Well logic on Limerick was about Limerick port. However after they had decided on tunnel it was announced that there were plans to move the port out to Foynes. One hand not knowing what the other does.

Likewise in Cork the harbour is main reason they went with tunnel otherwise they would have to gone with either a lifting bridge or a high level bridge. If you look at the plans for the "Eastern Bypass" of Dublin they talk bout three different options for crossing Liffey:

• Tunnel
• High-level (Mounmental) bridge
• medium-level opening bridge

monument

dubhthach wrote: »

If you look at the plans for the "Eastern Bypass" of Dublin they talk bout three different options for crossing Liffey:

• Tunnel
• High-level (Mounmental) bridge
• medium-level opening bridge

One road project in its current form which has less changes of being built than Metro West.

And, for all its flaws, at least Metro West has a nicer looking bridge!

dubhthach

monument wrote: »

One road project in its current form which has less changes of being built than Metro West.

And, for all its flaws, at least Metro West has a nicer looking bridge!

Indeed but I'm just putting it as an example of how plans for major roads interact with dockland areas.

Carawaystick

It'd be largely due to navigation of the waterway. Like on the barrow bridge for New Ross port there's an opening bridge and same in Waterford city. but for the new cable stayed bridge over the Suir, the height of the deck would be greater than the highest ship which would pass under going to Fiddown (If they still go there.)

An opening bridge has a much lower throughput ( cos of the road block when its open)

There would be historical heights of ships navigating a waterway, so for New Ross, tall sailing ships would have prevented/ made uneconomic a rail bridge high enough to allow them through.

re. the shenanigans at Limerick Tunnel/port I wouldn't be surprised.

antoobrien

veryangryman wrote: »

Ive always wondered what dictates whether to build a tunnel over a bridge for river/lake crossings.

In a nutsehell costs and environmental impact are the wo major factors.

There was a proposal to have a tunnel under the Corrib for the part of the GCOB that's with the ECJ (which Gromless nominated as a cSAC after PP had been granted by ABP). It was rejected by the County Council as being (a) too expensive and (b) having a bigger impact on the Limestone Slab than a bridge.

Mc Love

I always thought that a bridge would have been better than the Shannon tunnel!