The other 12tph on Crossrail (GWML side)

[mr_jrt]

Notice I used the word "practical". That means cost-effective. i.e. reasonable costs in relation to potential benefits.

And even if you did passively provide, you're making the assumption that the 3 curving turnback sidings work operationally as well as the proposed arrangement at Old Oak Common (which they may not if they are longer and/or slower, so might be detrimental to Crossrail operation until such a time that the remote chance it ever went up the NNML was realised)

...and my point is given that the platforms are identical in either scenario, the decision to do away with the flyover was nothing to do with it being the only cost effective way to provide the required platforms. It may well be a more cost effective way of providing the turnback sidings, but as far as I'm aware the platforms are the same in either scenario, thankfully. At least that means it could be built later, abet with far greater cost and disruption.

 

[Ianno87]

...and my point is given that the platforms are identical in either scenario, the decision to do away with the flyover was nothing to do with it being the only cost effective way to provide the required platforms. It may well be a more cost effective way of providing the turnback sidings, but as far as I'm aware the platforms are the same in either scenario, thankfully. At least that means it could be built later, abet with far greater cost and disruption.

It's a balance between extra cost and impacts now for something that (in my opinion) has a low likelihood of happening, or accepting more cost and disruption later if you do eventually choose to do it. I suggest even building a flyover now would have some additional disruption compared to the "standard" build of Old Oak Common (which, to my untrained eyes) could involve a relatively simple staged build from one side of the GWML to the other).

 

[cactustwirly]

They're perfectly well suited for the Readings, because (unlike Thameslink from Bedford due to the rather limited EMR service there) nobody will actually use them to travel from Reading to London or vice versa, any more than they presently (don't) use the all stations stopping DMUs. They are for local journeys connecting with the faster (80x and Electrostar) trains.

The situation, time-wise, is similar to Watford Junction - hardly anybody will use LO to go to London from there (taking an hour), they'll use the fast LNR services (taking 20 minutes).

It's not like the LO to Watford, it's more like the LNR services to Milton Keynes or Thameslink.
They should have got a 700 specification.
There is a significant flow from Twyford, Maidenhead and Slough to Paddington for which they are unsuited.

 

[mr_jrt]

It's a balance between extra cost and impacts now for something that (in my opinion) has a low likelihood of happening, or accepting more cost and disruption later if you do eventually choose to do it. I suggest even building a flyover now would have some additional disruption compared to the "standard" build of Old Oak Common (which, to my untrained eyes) could involve a relatively simple staged build from one side of the GWML to the other).

I don't disagree with you there - it had a low chance of happening in the first place, and once Crossrail is operating the disruption involved in bulding it later will probably prove untenable. If I'm honest, I'm not even sure how you could do it later. Even if you connected up one of the central turnbacks so you could disconnect the northernmost line to build the flyover, given the site constraints the alignment of the western end where it would need to fall to meet the GWML would almost certainly impinge on the running lines.

Though if it does in fact end up having room at the western end, then it doesn't really prevent the staged build you describe, so there's that.

 

[JN114]

A number of things:
* there is a single line into Heathrow Airport Terminal 4
* there are conflicting movements between the Terminal 4 and Terminal 5 branches
* the ideal operation for Terminal 5 is to always have a Heathrow Express train in the platform and allow time for alighting and boarding to be separate processes.

10tph into the Airport really ought to be sufficient, regardless of the flexibility of the grade separated junctions with the main and relief lines.

A huge limitation on airport branch capacity is escape shaft access.

The signalling sections are laid out so as not to overwhelm any one escape point by having more than 2 trains evacuate to the same escape shaft simultaneously.

To increase the number of signalling sections you would need to drill more escape shafts down from the surface.

 

[Ianno87]

To increase the number of signalling sections you would need to drill more escape shafts down from the surface.

And that's of only very limited headway benefit if you're still constrained by the train in front sitting at CTA for at least 90+ seconds to exchange passengers.

Notwithstanding the obvious point about where you'd physically locate shafts....there's a minor regional aerodrome sitting directly above a good stretch of the tunnel (for example).