Posted 28th June 2019 | 7 Comments

Damp Severn Tunnel has put electrification in doubt

ELECTRIFICATION equipment inside the Severn Tunnel is deteriorating so quickly that trains may have to use diesel mode when running through the 6km structure.

At the moment, the switch from electric to diesel traction on down trains takes place at Bristol Parkway, but it had been hoped to complete electrification to Cardiff later this year.

However. it has emerged that recently-installed earthing straps connected to the overhead conductor rails inside the tunnel are already breaking down. Network Rail had estimated that they would be all right for 25 years.

The first signs of trouble were reported last year.

The problems are due to the highly humid, saline atmosphere inside the tunnel. Pumps remove more than 60 million litres of water a day, which come from the ‘Great Spring’, and there are drainage tunnels under the main tunnel that take water to the pumps at Sudbrook, on the eastern side. Even so, conditions inside the tunnel are always unusually damp, no matter what the weather might be at either portal.

One immediate solution would be to use the diesel engines of the bi-mode Intercity Expresses when passing through the tunnel, but Network Rail has drafted in electrification specialists in a bid to find a longer-term remedy.

The DfT said it was ‘aware of an issue’ and that an investigation is under way to ‘resolve this as quickly as possible’.

In the meantime, Network Rail said it was still on course to be ready for an improved GWR timetable between London and South Wales in December this year.

Reader Comments:

Views expressed in submitted comments are that of the author, and not necessarily shared by Railnews.

  • jak jay, surrey

    Wonder how the Swiss/German/French/Italian railways manage in their tunnels?! Britain invented the railways and 180+years cant run a bath!!
    [The Severn Tunnel is a special case, because 60 million litres of water need to be pumped away every day. Most railway tunnels, including those on the continent, are bored through hills or mountains. Tunnels under rivers are less common, although not of course unknown, including a number on London Underground, where there were concerns some years ago about the state of the Bakerloo under the Thames. The Severn's 'Great Spring' has always caused particular problems.--Ed.]

  • James Blackham, Chelmsford

    This would put an end to the open access bids to run 91s from London-Cardiff.

  • Andrew Gwilt, Benfleet Essex

    At least Class 800 Bi-mode trains have no problem despite the electrification has only reached as far as Bristol Parkway.

  • Jonathan Brain, Potters Bar

    Long term plans for a combined motorway / rail bridge like the Danish and Swedish?

    Resurrect the Severn barrage idea including motorway / rail links in the scheme.

    This is sign of a larger national malaise than NR electrification incompetence!

  • Jez Milton, Manchester

    The incompetence of NR on GW electrification seemingly knows no bounds. It never ceases to amaze (and disappointment).

    Who would have thought the OLE in the Severn Tunnel would need to be robust enough to handle the salt water that has always leaked in (and been pumped out)?!?

  • david c smith, Bletchley

    Perhaps an example that it could have been better for the dual - mode Azumas to have energy storage using batteries rather than auxilliary diesel - alternators?Total costs , including maintenance , may be considerably lower . For most electrification "gaps", a full line speed capability on diesel power that is only utilised for a few miles seems unnecessarily expensive.

    A couple of services that couldn't use battery "gap bridging" due to the gap being too long would be Paddington to Devon / Cornwall and King's X to Aberdeen , where another approach is needed.

  • les upham, Bristol

    why not build a railway bridge like the 2nd severn bridge crossing and do away with the tunnel