In article , Paul Corfield
writes
but your proposal reverses the direction of the *single track* loop line
between T123 and T4. You are assuming that the train reverses at T4 and
goes back to T123. This would mean bi-directional working on a single
track line which would severely reduce the headway to T4.

Increase the headway, reduce the frequency.

According to a WTT I have, the running time from T4 to T123 is 5
minutes. So even with stepping back of drivers, you're talking at least
11 minutes between trains, so 5.5 tph total.

In that WTT, the service on the Heathrow branch is 12 to 15 tph for most
of the time (including the peaks). If one-third of the trains served T4,
as is planned, that would be 4 to 5 tph.

So it's about doable, but it would be a very fragile timetable. If a
train is delayed for less than 5 minutes, the next T4 train won't be
able to get out of the platform at T123 and on to the single line before
it blocks the next T5 train. So you'll need to change destinations,
which means announcements and annoyance as people get off with all their
luggage so that they can get on the next one.

I appreciate you can argue about whether to go clockwise or
anti-clockwise round the loop but it is too late to change things now.

Anti-clockwise means rebuilding at Hatton Cross, and eastbound trains
from T4 having to cross the path of westbound trains.

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Clive D.W. Feather, writing for himself | Home:
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