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Author Topic: A new Severn tunnel - or other crossing?  (Read 9735 times)
ellendune
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« Reply #45 on: October 26, 2021, 07:32:34 am »

Long tunnels are inherently vulnerable to fire.

And bridges are vulnerable to impact by shipping as in the case of a certain previous Severn railway bridge. 
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eightonedee
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« Reply #46 on: October 26, 2021, 08:36:49 am »

Quote
And bridges are vulnerable to impact by shipping as in the case of a certain previous Severn railway bridge.

....but I doubt that anyone would now propose a bridge consisting of a series of relatively short spans between several towers as in that structure.
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broadgage
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« Reply #47 on: October 26, 2021, 09:52:13 am »

Long tunnels are inherently vulnerable to fire.

And bridges are vulnerable to impact by shipping as in the case of a certain previous Severn railway bridge. 

Yes, but this proposal was for a substantial barrage of stone and concrete that would resist damage from a ship. With lock gates in the middle for ships, and a bridge under which ships could pass.
An out of control ship might damage the lock gates but not the bridge.
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A proper intercity train has a minimum of 8 coaches, gangwayed throughout, with first at one end, and a full sized buffet car between first and standard.
It has space for cycles, surfboards,luggage etc.
A 5 car DMU (Diesel Multiple Unit) is not a proper inter-city train. The 5+5 and 9 car DMUs are almost as bad.
johnneyw
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« Reply #48 on: October 26, 2021, 11:05:50 am »

The problem with the Severn Estuary was always the issue of silting up and turning the whole expanse into flood plain.  I'm not sure anyone has come up with a practical, economically viable solution to that.  As for the impact on natural habitats....
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TonyK
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« Reply #49 on: October 27, 2021, 03:58:42 pm »

A causeway would, as pointed out before, be phenomenally expensive. The risks, both economic and environmental, can be modelled, but have a great degree of the unknown about them. The much smaller Rance barrage has caused silting, and seen off a couple of species that previously lived in the estuary. Whether the power it produces swings the balance to positive depends on whether you are talking to an ecologist or a civil engineer, but the effects came as a slight surprise. A Severn Barrage could spring much greater surprises, or it might be perfectly fine, but the uncertainty is probably more than enough to put off private investors.  Government knows that if it promoted the barrage, the battle between green power lovers and nature lovers would go on for years before a decision could be taken, even longer than HS2 (The next High Speed line(s)) or Hinkley C. For these reasons, I doubt it will happen.

The first tunnel seems to have been a mistake that won't be repeated, even if the engineers of the day did get away with it. A new one would, as stated earlier, need a much more sophisticated design of twin bores or escape towers mid-river, and extra Severn bores don't come cheap.

That leaves a bridge as the favourite. I doubt that it could incorporate wind turbines, as they need regular maintenance, and there is a risk of bits dropping off. Not a high risk, but enough to preclude a rail service. I can't see the benefit would justify the cost as things stand, even though the engineering would be much simpler than for a barrage or tunnel.
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Now, please!
eXPassenger
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« Reply #50 on: October 27, 2021, 06:26:35 pm »

If we were Danish we would have put rail lines on the second Severn crossing (Prince of Wales Bridge).
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