Size of Northern Line Extension vs Jubilee Line Extension tunnels

HSTEd

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Does anyone know the specific rationale for the escalation from 4.35m tunnels on the Jubilee Line Extension to 5.2m on the Northern Line extension?

My understanding was that the JLE tunnels did include a continuous evacuation walkway, which makes the extra size seem a little odd.

Have standards on the widths of walkways increased since then?

Or is this just improving tunneling technology changing the cost benefit analysis on tunnel sizing?
 
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Hadders

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As I understand it the walkways on the Jubilee Line Extension aren't large enough to be considered as an evacuation walkway.
 

bramling

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As I understand it the walkways on the Jubilee Line Extension aren't large enough to be considered as an evacuation walkway.

Yes I think this is the reason. Two issues - firstly the JLE walkway isn't wide enough for wheelchairs, and secondly there isn't room for two people to pass - which introduces a problem as you have two potentially conflicting flows, namely passengers attempting to escape and firefighters attempting to reach a location.

To be honest it all strikes me as a little overkill when we still have 19th century Tube lines and stations with none of this, but there we go.
 

D365

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To be honest it all strikes me as a little overkill when we still have 19th century Tube lines and stations with none of this, but there we go.
Well yes but we have to start somewhere.
 

swt_passenger

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Out of interest does anyone know if the new Northern line tunnel through Bank will be fitted with the same walkways?
I think from the video I’ve seen it will be big enough, but it’s a different flat bottom shape as it’s mined and spray lined rather than dug with a TBM. Is the new bit long enough to justify an escape route, I suppose it probably is north of the Bank platform, but I think it rejoins the existing tunnel fairly quickly at the south end.
 

rebmcr

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I am sure you are right but how can you tell from the video?

I can’t see any potential fixing points
The position and height of the valance hanging from the ceiling, which blocks off airflow from the void above the tracks.
 

alf

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Thanks.
I assumed that valance was there to support high quality lighting over the door platform interface.

I shall check if the Jubilee line platform doors have a similar valance.
 

rebmcr

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I shall check if the Jubilee line platform doors have a similar valance.
On the Jubilee line an older concept is installed (Platform Edge Doors rather than Platform Screen Doors), without airflow separation.

For examples contemporary to this Battersea Extension, look at the Elizabeth line.
 

Mikey C

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There appears to be passive provision for future fitment of platform screen doors.
I assume they're part of the standard TfL platform spec now, as the chances of the Northern Line in general ever getting platform edge doors must be pretty remote
 

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