Do you understand the issues on the GW? Firstly the Relief lines are cleared for 85/90mph running already. I have quoted the notional peak period Crossrail timetable in post No. 1748. There will be 10 trains per hour on the Reliefs leaving the Crossrail tunnels at Paddington. Are you suggesting that your fast train to Slough is one of these trains or an additional one?
I am suggesting the GW relief timetable be torn up and a new one written from scratch to account for the epochal changes brought about by Crossrails introduction.
Ideally the relief lines would be pure ETCS and fitted with ATO for maximum efficiency, and no other trains would use them outside of disruption.
Crossrail is sold as being a super-tube-line, it needs to act like one in service density terms.
I suggest that you consider how one could also continue to serve the other stations on the route with a frequency and journey times which are at least equivalent to that which they now enjoy if either an extra non-stop is introduced or stops are removed from one of the 10. If the latter then you will have to explain to the people using the trains from, among others, Ealing Broadway, Hanwell, Hayes, Langley and Iver that in spite of the Government having spent billions on Crossrail their train service has been reduced.
How about this:
If we go to the
Bombardier HS2 ETCS capacity study [the most easily available headway calculation document I have at the moment], we see a rather interesting curve on page 6 indicating headway against train speed.
At ~90mph/145kph the technical headway time of 75 seconds at ~800m section lengths, well within the capabilities of existing technology. That is still only ~25 blocks between Hayes and Harlington and Paddington so its hardly bank breaking. Moving to 400m sections would shorten the headway to something like 60 seconds apparently, which would provide more margin but be more expensive.
We should only load the line up to 3/4 its theoretical capacity, so our timetable headway is 100 seconds. Or 36 notional paths an hour if all trains were flighted non-stop and there were no platforming issues.
My best guess estimate is that the Heathrow Express can complete a run non-stop to Hayes and Harlington is roughly 15 minutes based on its ~21 minute total travel time.
The Heathrow Connect takes roughly 20 minutes from departing Paddington to Departing Hayes and Harlington for the run to the airport, and would take ~21 minutes once the new stop at Acton Main Line is included.
21 minutes translates as a 6 minute timetable deficit.
This is important as it defines the size of our 'flighting envelope'.
I propose a flighting scheme of:
1. Non stop to Reading [grab Reading commuter traffic]
2. First stop Slough train
3. Non-stop train to Heathrow (although this being first would reduce the number of points movements, doing it this way would slightly spread the load by allowing the previous slow train more time to reach Heathrow before being run down by the express)
4. First stop Hayes and Harlington towards Maidenhead
5. The all stops train to Heathrow.
6 minutes plus 500 seconds is ~14 minutes. So you could run the entire thing on a 4 flight-per-hour cycle.
If you shorten headway to 60 seconds with the extra signal blocks (which could be put in at minimal cost during the current resignalling works) then you end up with 6 minutes plus 360 seconds, which is 12 minutes. And then thanks to your 75% capacity pad you could run at a 5fph cycle.
But you might just want the extra capacity to improve the resilience of the 4fph cycle.
4fph translates as 20 trains per hour.
So in order to make this practical you would have to bring forward the 30+tph Crossrail proposal, as you would otherwise have to hold up trains to build up the flights. At 30tph there is very little of that, you just notch out the flights by turning back some of the trains.
Either way, it turns the line into some sort of crazy high capacity Metropolitan line. And every station receives at least 4 trains per hour. And many of the outer stations could have more if you wanted.
Oh, and off-peak there are several stone trains running to Acton Yard, some of which weigh up to 4,000 tonnes and the corresponding westbound empties, some of which run in the shoulder peak. The Freight Operating Companies also have track access contracts. And there are some automotive trains from Purfleet to Cowley which also have to be fitted onto the Reliefs.
Run them on the fasts.
Running everything on them fast to Reading turns into into HS2, giving you more paths than you really need by a significant margin. (Do you really need 18 125mph paths from Pad to Reading?)
If you attach a suitable electric locomotive to the freight trains at Reading you can haul them at high speed and simply notch out a path every hour in each direction by withdrawing two or three of the high speed paths.
Or you could just give them a bung to run at night. Your choice.