In article , asdf
writes
It's the latter AIUI - i.e. trains will run either:
(1) Hatton Cross - T4 - T123 - Hatton Cross in the loop
or
(2) Hatton Cross - T123 - T5 where they'll terminate and then reverse.

That's forced by the physical layout:

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

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).

Slightly more radically, they could even close part of the loop,
running trains either CL-HX-T123-T4-T123-HX-CL, or CL-HX-T4-HX-CL
(where CL = Central London and HX = Hatton Cross). This would simplify
the line map and service pattern.

The latter has the above problem. The former has the problem that the
single line between T3 and T4 puts heavy constraints on how frequent the
trains can be. Probably 3tph would be the limit.

[Memory says this was covered in Underground News recently.]

--
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