In article ,
lid (asdf) wrote:

OK, so it'd have to be "T5 via T123" and "T123 via T4". T4-bound
trains with a T5 service following a few minutes behind (close
enough that it will arrive at T123 first) could be shown as "T4 only".

How close behind a via T4 train would a T5 terminator have to be for the
latter to get passengers to T123 first?

--
Colin Rosenstiel

Colin Rosenstiel wrote:
In article .com,
() wrote:

Clive D. W. Feather wrote:
That's forced by the physical layout:

T5 ---------*-- T123 ---------------* HX ----- London
/ /
| /
\ /
\-------- T4 -------/


Probably a stupid question, but why was the decision taken to
construct the line in that layout, rather than extending the loop so
trains would call HX, T4, T5, T123?

Geography? Have you looked where Terminals 4 and 5 actually are?

Thanks for that informative reponse.

Are the terminals really so far apart that a three station loop would
have been impractical? It just seems a more logical service pattern
than some loop, some terminating.

Patrick

wrote:

Geography? Have you looked where Terminals 4 and 5 actually are?


Thanks for that informative reponse.

Are the terminals really so far apart that a three station loop would
have been impractical? It just seems a more logical service pattern
than some loop, some terminating.

Look at Heathrow on Google Map:
http://maps.google.com/maps?&om=1&z=...+airpo rt,+uk

You can see the new T5 taking shape about 1 ½ mile or someting west of
the T 1-2-3 station.

If you then look at the locations of T1-2-3, T4, T5 and Hatton Cross
stations I think you realize that a big loop through all of the stations
would not be realistic.

But the again you have a point about the service pattern getting far
more complex to the passangers, maybe it would have better to cut of the
south-eastern part of the current loop and drive the T4 trains via
T1-2-3 and then terminating and reversing at T4. That would give
HX-T123-T4 or HX-T123-T5 services, both terminating and reversing out
the same way they got in and easy to read and understand line diagrams.

--
Olof Lagerkvist
ICQ: 724451
Web: http://here.is/olof

On 27 Sep 2006 02:27:37 -0700, wrote:


Colin Rosenstiel wrote:
In article .com,
() wrote:

Clive D. W. Feather wrote:
That's forced by the physical layout:

T5 ---------*-- T123 ---------------* HX ----- London
/ /
| /
\ /
\-------- T4 -------/


Probably a stupid question, but why was the decision taken to
construct the line in that layout, rather than extending the loop so
trains would call HX, T4, T5, T123?

Geography? Have you looked where Terminals 4 and 5 actually are?

Thanks for that informative reponse.

Are the terminals really so far apart that a three station loop would
have been impractical? It just seems a more logical service pattern
than some loop, some terminating.

If I recall correctly, the T4 loop does include a straight section
somewhere near where, at the time of it's construction, they expected
a future T5 to be. However the T5 that's being built is considerably
larger and in a different place than the T5 foreseen back then.

I've a vague feeling that the newish Heathrow Express tunnels also
made provision for a T5 station where the original plan for it was,
however that provision too has turned out useless.

In article , I wrote:
ISTM that it would be better to reverse the direction that trains go
around the loop (and still lay over at T4).

If you do that then London-bound trains will have to cross the
westbound line on the level, putting constraints on operations. Anyway,
I don't think that there's room west of Hatton Cross for a crossover to
the eastbound track (the junction is officially 90m from the mid-point
of the station, and a crossover requires at least 40m). So now you're
talking major reconstruction as well as resignalling the loop (which is
signalled one-way only).

I was there today: there is *definitely* not enough room for a crossover
without major tunnelling - the points are less than a car length from
the stopping point. But the westbound platform is signalled reversibly
and there's a crossover at the *east* end. So in theory you only need to
resignal the loop.

However, I'm still unconvinced that the pathing to fit eastbound trains
between the westbound ones is workable, especially as this approach
means the trains need to stop, not just run through.

--
Clive D.W. Feather | Home:
Tel: +44 20 8495 6138 (work) | Web: http://www.davros.org
Fax: +44 870 051 9937 | Work:
Please reply to the Reply-To address, which is:

Peter Frimberley wrote:
I've a vague feeling that the newish Heathrow Express tunnels also
made provision for a T5 station where the original plan for it was,
however that provision too has turned out useless.



The Heathrow Express provision is being used! It is a spur by Central
station, where the current Heathrow Connect trains reverse (not in
passenger use, obviously). The spur, which was put in during the
original construction, is being extended to Terminal 5 as originally
planned.

PhilD

--

In article .com,
writes
Probably a stupid question, but why was the decision taken to construct
the line in that layout, rather than extending the loop so trains would
call HX, T4, T5, T123?

Terminal 5 is a *long* way west of Terminals 123 (2.3km). The run from
Terminal 4 round to T123 is already 4.4km, and most of that would have
to be abandoned. So you'd need about 6km of new tunnel for the loop as
well as the 2km actually dug.

--
Clive D.W. Feather | Home:
Tel: +44 20 8495 6138 (work) | Web: http://www.davros.org
Fax: +44 870 051 9937 | Work:
Please reply to the Reply-To address, which is:

In article ,
Colin Rosenstiel writes
How close behind a via T4 train would a T5 terminator have to be for the
latter to get passengers to T123 first?

The advertised running times are 3 minutes from Hatton Cross to T4, and
5 from there to T123. I expect it's also 3 minutes from Hatton Cross
direct to T123. So the answer is 4 minutes.

--
Clive D.W. Feather | Home:
Tel: +44 20 8495 6138 (work) | Web: http://www.davros.org
Fax: +44 870 051 9937 | Work:
Please reply to the Reply-To address, which is:

Olof Lagerkvist wrote:
wrote:
Are the terminals really so far apart that a three station loop would
have been impractical? It just seems a more logical service pattern
than some loop, some terminating.

Look at Heathrow on Google Map:
http://maps.google.com/maps?&om=1&z=...+airpo rt,+uk

You can see the new T5 taking shape about 1 ½ mile or someting west of
the T 1-2-3 station.

If you then look at the locations of T1-2-3, T4, T5 and Hatton Cross
stations I think you realize that a big loop through all of the stations
would not be realistic.

I see what you mean; it is a bit further away than I thought. You
still could have done a big loop, maybe giving Stanwell its own tube
station as well. But I guess that would mean far longer journey times
for passengers getting on at Terminal 4.

Patrick

On Wed, 27 Sep 2006 08:21 +0100 (BST), Colin Rosenstiel wrote:

OK, so it'd have to be "T5 via T123" and "T123 via T4". T4-bound
trains with a T5 service following a few minutes behind (close
enough that it will arrive at T123 first) could be shown as "T4 only".

How close behind a via T4 train would a T5 terminator have to be for the
latter to get passengers to T123 first?

Depends how long the T4 trains lay over at T4. Add to that the time
difference between going round the loop and going direct to T123, and
you have your answer.