In message
-septe
mber.org, Recliner wrote:
But in this case, the 73TS were built while the Heathrow extension was
under construction, and a large enough fleet to cover it was ordered.
Without that extension, the order would have been for a significantly
smaller fleet.

Actually, I don't think so. The order was for 87.5 trains. I reckon that
the extension only needed 4 of those.

I'd guess more, probably six or seven in the peaks. There are four
stations, and there are usually two in the T5 station at any time, and
usually one in the T4 station or at least in the loop.

Irrelevant. The stock was ordered in 1971 and delivered starting in
1974. The first plans for the present T4 didn't start until 1977 and the
loop wasn't authorized until 1980. So neither of these would have been
included in the calculations for the order.

There's another pair
at or near Hatton Cross, and another pair at or near Heathrow Central.

That's the four. Actually three; remember that there's no longer a train
sitting for ages at Hounslow West.

Uxbridge doesn't get a 12tph service. It's more like 6tph in the leaks,
less in the off-peak.

The Heathrow branches get a much more intense service than Rayner's Lane
branch, which has lost services in favour of the two Heathrow branches.
Probably six or seven of every ten trains running west of Acton Town heads
for one or other of the two Heathrow branches.

Looking at the evening peak, there's 23 trains leaving Gloucester Road
between 17:00 and 18:00, split 11 to Heathrow (6:5 between the T4 and
T5) and 12 towards Rayners Lane (7 to Uxbridge). There's 23 between
18:00 and 19:00, now split 13:10 (still 7 to Uxbridge). That's not "much
more intense".

That's
about 75 trains. The rest allow you to thicken the service in the peaks
and provide spares.

Ah, another source says the current service uses 76 trains on Saturdays
and 68 on Sundays.

So almost 10% of the service fleet are on the Heathrow extensions at any
time. Allowing for a spare, that means about eight trains in all are needed
for the service west of Hounslow West.

Yes, *but* that wasn't the basis they were ordered on.

So the stock order was very probably based on that 12 tph figure.

As I said, 3/4 trains is an underestimate. It's more like six. You seem
to have forgotten T5, which usually has two trains in the station or
sidings, and T4, which always has a train in the station or loop.

But those other trains have come from better utilization. The stock was
ordered on the assumption of just T123 or *possibly* thinking ahead to a
T4 station on the Stanwell sewage farm site to the south west.

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Clive D.W. Feather | Home:
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