At what point do we rebuild the tube from scratch?

[Comstock]

Obviously the cost would run into many billions. The indirect economic cost could be many times that. But can anyone see a scenario where they eventually rip out the tube, make the tunnels bigger and re-lay it? It would solve a lot of problems, from capacity to the heat of mid summer.

Is there any kind of ultra long term planning to cover this eventuallity, or is the tube destined to be patched up forever?

 

[gordonthemoron]

They wouldn't do that, they'd either build new lines, hopefully to better specs, or improve bus/tram routes like Berlin has done

 

[edwin_m]

I can't see it happening, unless the actual tunnels become dangerous (will the cast iron segments eventually corrode?) and there isn't an easier solution such as grouting or some kind of systematic replacement. While the Tube rolling stock is obviously highly non-standard, they have enough of it that the supply industry should be able to bid for fleet replacements without a huge cost premium. Things such as tunnel cooling can be addressed piecemeal, and in fact I read something the other day suggesting the main problem was trains coming in from surface sections having undergone solar heating and could be addressed by reflective windows and underframe paint.

 

[Chris M]

Cast iron tunnel segments can corrode in at least some conditions, but tunnel segments can be (and have been) removed and replaced during night time and weekend closures. They did this on the Jubilee line around Bond Street a few years ago (although I think they were concrete rather than cast iron segments).

As for the OP's suggestion, that will never happen.Building new lines would not only be easier and cheaper, but it would also give much greater capacity, e.g. if a mainline size tunnel has 25% more capacity* than a tube tunnel then an oniine upgrade would get you 25% more capacity, but a new parallel tunnel would get you 125% more capacity as you will still have the existing line. And even if you did somehow find the money to expand the original tunnels, you couldn't just enlarge them in situ as there are plenty of places where expanded tunnels just wouldn't fit past each other and/or other infrastructure - they had to thread the Crossrail tunnels through Tottenham Court Road with only a few centimetres clearance to the existing tunnels for example.

 

[Snow1964]

There have been a few short sections where the tunnels were enlarged (and of course most of the original City and South London from near Borough to Stockwell), but that tends to be for specific reasons of tight clearances.

I'm sure in 1930s there used to be engineering trains, overnight park in tunnel, remove some upper ring sections, pare back the clay, reinsert sections with extra cast iron section (about 20cm wide). Don't get a perfectly round tunnel, but did ease some clearances on curves. Was also used on Central Line when platform tunnels extended to ease the gradients (as line was built with inclined tunnels approaching and leaving platforms to aid acceleration and deceleration). Even today on most Bakerloo, Piccadilly and Central Line platform tunnels can see a kink in platform lining where platform tunnel extended around the original running tunnel.

On many 1930s extension sections, stations have platforms designed for 8 or 9 standard cars so are longer than trains. Some 1930s relocated stations like Aldgate East also built with longer platforms.

But not worth trying to increase tunnel diameter throughout, much easier to build new line.

However there may be a case for platform extensions to be resumed, for instance many Piccadilly line platforms are now longer than the 6 car trains, but only makes sense if trains are being replaced. Unlikely to be full width, but sufficient to reach last door without causing congestion. Some of these extra bits of platforms are now fenced at front to allow DOO monitors and mirrors, but latest trains have moved this to in cab screens so could be reused with new trains. Maybe increasing frequency to 36 tph is cheaper than small platform tunnel extensions, as either way have to buy extra carriages.

 

[mark-h]

There is also the issue that if major work is carried out the system may be required to build to current standards. Enlarged tunnels would have to be made even bigger to accommodate an evacuation walkway (such as in Crossrail and the Northern Line extension). Stations would need to be made accessible with independent fire escapes from each platform. All of this would increase the cost of the upgrades beyond the point that the benefit is justifiable.

Disruption would also have to be considered, a major upgrade would result in lines being closed for years (the 1970s modernisation of the Glasgow Subway took 3 years without changing the tunnel size or making any stations accessible). Closing a London Underground line for that length or time would result in serious disruption and would result in serious overcrowding on other lines.

 

[Bald Rick]

Also worth bearing in mind that 100+ years of development around most tube tunnels in London means there are a lot of things very adjacent to the tunnels which can’t be moved. Crossrail is just one example.

 

[theking]

Think there is zero chance ever, the cost would just be too exorbitant.

The best you'll get is new lines to relieve congestion or maybe platform extensions if they ever thought about extending trains..

 

[Comstock]

Think there is zero chance ever, the cost would just be too exorbitant.

'ever' is a very, very long time, though.

I'm not seriously going to ask people to speculate about 10,000 years time, that would just be daft. But some Japanese corporations have 200 year plans. That's the sort of timeframe I'm considering.

 

[Busaholic]

I think even Utopians would rightly baulk at this: we are where we are, for better or worse, and just have to make the best of it. Does anyone seriously want to see a Bakerloo 2100?

 

[mr_jrt]

What you also have to consider is that the space available underground isn't infinite. There may come a time when the benefits of new lines outweigh keeping the old ones. You can of course go deeper to a point, but then you have to get the passengers to and from the surface at the stations!

 

[100andthirty]

in the last 100 years the average height of men - who are, on average taller than women - has increased by 10 cm. Already there are a number of people who can't stand upright in a tube train. Whilst the rate of increasing height has slowed, I can see a time at some point in the future when a significant proportion of customers can't stand upright anywhere in a tube car. I think there might be the opportunity to squeeze a little extra headroom on new trains, but it won't be easy. If this happens there will be pressure to rebuild the lines or build new ones. I think we'll be OK for another century - but then again, I won't be around for anyone to say "I told you so"!

 

[edwin_m]

in the last 100 years the average height of men - who are, on average taller than women - has increased by 10 cm. Already there are a number of people who can't stand upright in a tube train. Whilst the rate of increasing height has slowed, I can see a time at some point in the future when a significant proportion of customers can't stand upright anywhere in a tube car. I think there might be the opportunity to squeeze a little extra headroom on new trains, but it won't be easy. If this happens there will be pressure to rebuild the lines or build new ones. I think we'll be OK for another century - but then again, I won't be around for anyone to say "I told you so"!

There was an idea floated a few years ago to re-build the Tube with lower train floors and platforms using the same technology as in low floor trams, therefore increasing the height inside the trains. I'm not sure where they planned to put all the traction and other equipment, which goes under the floor in a Tube and above the ceiling in a low-floor tram. But if interior headroom needed to increase then something like this would be easier (or perhaps I should say less difficult) than boring out the tunnels to a larger diameter.

 

[100andthirty]

Lowering the floor a little bit - max 5 cm - (as I suggested above) might be feasible at least away from the bogies. Low floor tramways put equipment on the roof. This is not feasible on tube trains with their very curved roof profile.

 

[mr_jrt]

Of course, when originally built the tube trains had locomotives and simple carriages as the traction equipment was so large. It's not inconceivable to return to that arrangement now that the driver can use CCTV to check the doors - indeed, there are already numerous locations where the train is longer than the platform, so what difference would it make to have a loco off the platform, with drivers accessing it when needed via an inter-carriage walkway? https://en.wikipedia.org/wiki/Londo...ia/File:Central_London_Railway_locomotive.png

 

[Deerfold]

in the last 100 years the average height of men - who are, on average taller than women - has increased by 10 cm. Already there are a number of people who can't stand upright in a tube train. Whilst the rate of increasing height has slowed, I can see a time at some point in the future when a significant proportion of customers can't stand upright anywhere in a tube car. I think there might be the opportunity to squeeze a little extra headroom on new trains, but it won't be easy. If this happens there will be pressure to rebuild the lines or build new ones. I think we'll be OK for another century - but then again, I won't be around for anyone to say "I told you so"!

Whilst we have increased in height by 10cm over the last 150 years, the increase has pretty much levelled out and unlikely to increase much more - the changes appear to be largely a result of improvement in early childhood nutrition.

 

[AM9]

Whilst we have increased in height by 10cm over the last 150 years, the increase has pretty much levelled out and unlikely to increase much more - the changes appear to be largely a result of improvement in early childhood nutrition.

And now childhood nutrition is expanding many of them horizontally, thereby reducing the headcount capapcity of the tube rolling stocl.

 

[philthetube]

Interesting thought, however would require considerable rebuilding at many points where the loco would obstruct points etc, also many dopots would need a complete rebuild to increase stabling road length

can't see it happening though, huge costs for small benefits.