The same problem would exist with single deck stock, even narrow stock like U sets.
The double deck cars occupy virtually the same dynamic envelope as SD stock, the underfloor equipment filling the space that the lower deck occupies on DD stock.
With a circular tunnel the only way you’d get a walkway in would be to make the entire bore larger.
Tony
> On 6 Dec 2023, at 12:01, TP historyworks@...> wrote:
>
> I'm getting the picture that the Airport Line tunnels were not built "on the cheap", but because they decided that the technology had progressed sufficiently to build future rail tunnels using TBMs which have the advantage of lining the tunnels as they go and, judging by the metro lines, seem to be quicker than using roadheaders etc, then having to line the tunnels. The downside for double deckers of course is their vertical dimension as you say. That may have contributed to not being able to have a walkway inside the tunnel as the metro does, but as was mentioned above, they might have decided that, if work was required inside the tunnel, they could reroute trains onto the Illawarra surface tracks. I wasn't involved in the project post-approval so I have no insight into what happened subsequently.
>
> Tony P
>
> On Wednesday 6 December 2023 at 09:36:11 UTC+11 Tony Galloway wrote:
> It still has to meet standard structure/loading gauge clearances, but the round tunnel shape, of which about 15-20% is taken up by the track bed, means the tunnel walls are closer to the trains where the roof meets the sides of the cars, and lower where the fish bellies of the double deckers are close to the track.
>
> With this tightness there are no safe spaces for anyone on track where two trains are passing.
>
> Tony
>
>
>> On 5 Dec 2023, at 22:44, TP histor...@... <applewebdata://35C8F601-3E00-46FE-B1DA-D12E25556A8D>> wrote:
>>
>
>> If the line was tunneled with TBMs, resulting in lined tubular tunnels like the Sydney metro tunnels, I imagine that this would create a tighter clearance for double deck trains. All previous Sydney railway tunnels had vertical walls. Am I correct?
>>
>> Tony P
>>
>> On Tuesday, 5 December 2023 at 19:49:57 UTC+11 Tony Galloway wrote:
>> The type of tunnel construction precluded having refuges, and with the alternative route through Sydenham available, diversions were the easier option if anything failed in the tunnel.
>>
>> Apparently.
>>
>> Tony
>>
>> > On 5 Dec 2023, at 17:14, Matthew Geier mat...@... <>> wrote:
>> >
>> > On 5/12/23 16:59, Robert Taaffe wrote:
>> >> When the airport line was designed it was intended that it would never be maintained under traffic, only at night or during possessions.
>> >
>> > So the assumption was that things would only break on schedule ?
>> >
>> > Actually given the state of some of the Sydney Citadis already, I think that thinking is being applied to them to.
>> >
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