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 historyworks@...> 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...@... <applewebdata://BFFFD6A2-CD82-43A3-AF60-9160ABCF2418>> 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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