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Tube tunnels relay are not large. They vary a bit by line but in general they're really really small and severely limit the design of new trains. There's no way

Tube tunnels relay are not large. They vary a bit by line but in general they're really really small and severely limit the design of new trains. There's no way you'd fit two vehicles side by side in those tunnels, and they're not high enough to stack them either. Nor are they interconnected well enough to make one the passing lane. Have a look for yourself if you get to London, the entire tube system is mind-boggling.

Silhouette 11y ago
I'm from the UK and have been riding the Tube for decades. If we're talking about a hypothetical alternative transport system to be built underground and carry private vehicles potentially with single occupancy, you could probably fit four such vehicles within a cross sectional area not much bigger than the existing tunnels. The engineering practicalities would presumably still favour a round tunnel, which would be less efficient in space if you were running smaller vehicles in parallel, though. Then again, as I mentioned elsewhere, the cost of actually doing any of this in both time and money would be wildly prohibitive today and seems likely to remain so for many years to come, so this is all rather hypothetical anyway.
- lorenzhs 11y ago
  Right, sorry. If the tunnels were even 30cm wider this would indeed be a lot simpler, but as you say the cost of that would be wildly prohibitive in the foreseeable future. TfL would love it, though ;) Come to think about it, what would be the optimal layout of such an underground tunnel system for single-occupancy vehicles? The current system of changing lines and the station layout that results from it would no longer be a good fit, you'd have to come almost to a standstill. It could even be that reusing the tube tunnels would be less efficient than boring new tunnels in a future where tunnels can be bored "cheaply" with very little human involvement.
  - Symbiote 11y ago
    Are tunnels likely to get much cheaper? Compared to a lot of construction work it seems to be fairly automated already — take a look at some Crossrail videos [1] — so I'll bet a lot of the cost is design, planning and solving unexpected problems. And the cost of the machine. [1] https://youtu.be/X_ffeK8SIDo?list=PLF8E85417123BEF2F&t=66 https://youtu.be/X_ffeK8SIDo?list=PLF8E85417123BEF2F&t=66 (Quotes, roughly: 500,000 components in the tunnel boring machine, staff of 20 round the clock,
    - Silhouette 11y ago
      FWIW, my civil engineer friends once told me that the biggest problem with building something like this often isn't the tunnel itself, it's making sure you minimise damage to everything already built on the ground above. In this case, there is a lot of London up there, and causing subsidence under a road with average house prices in the millions would be a very expensive mistake.

Silhouette 11y ago

I'm from the UK and have been riding the Tube for decades. If we're talking about a hypothetical alternative transport system to be built underground and carry private vehicles potentially with single occupancy, you could probably fit four such vehicles within a cross sectional area not much bigger than the existing tunnels. The engineering practicalities would presumably still favour a round tunnel, which would be less efficient in space if you were running smaller vehicles in parallel, though. Then again, as I mentioned elsewhere, the cost of actually doing any of this in both time and money would be wildly prohibitive today and seems likely to remain so for many years to come, so this is all rather hypothetical anyway.

lorenzhs 11y ago
Right, sorry. If the tunnels were even 30cm wider this would indeed be a lot simpler, but as you say the cost of that would be wildly prohibitive in the foreseeable future. TfL would love it, though ;) Come to think about it, what would be the optimal layout of such an underground tunnel system for single-occupancy vehicles? The current system of changing lines and the station layout that results from it would no longer be a good fit, you'd have to come almost to a standstill. It could even be that reusing the tube tunnels would be less efficient than boring new tunnels in a future where tunnels can be bored "cheaply" with very little human involvement.
- Symbiote 11y ago
  Are tunnels likely to get much cheaper? Compared to a lot of construction work it seems to be fairly automated already — take a look at some Crossrail videos [1] — so I'll bet a lot of the cost is design, planning and solving unexpected problems. And the cost of the machine. [1] https://youtu.be/X_ffeK8SIDo?list=PLF8E85417123BEF2F&t=66 https://youtu.be/X_ffeK8SIDo?list=PLF8E85417123BEF2F&t=66 (Quotes, roughly: 500,000 components in the tunnel boring machine, staff of 20 round the clock,
  - Silhouette 11y ago
    FWIW, my civil engineer friends once told me that the biggest problem with building something like this often isn't the tunnel itself, it's making sure you minimise damage to everything already built on the ground above. In this case, there is a lot of London up there, and causing subsidence under a road with average house prices in the millions would be a very expensive mistake.