Boltar wrote:
Had to go to a meeting at Hangar lane today. After white city the
train just took off, we must've been doing 40-50 mph. How come the
other tube lines are so slow in comparison? The piccadilly plods its
way to acton town and the northern line between east finchley and
finchley central seemed to barely get above 25mph the few times I did
it last year. Why is the central line different?

B2003
The signalling on many older lines was not set out for high speeds - even
Hammersmith to Acton Town was designed for "Flag Switch Down" running (no
weak field on the motors - normal for in tunnel lines) although my own
experience was that the notices were usually ignored! The Met main was
signalled for fast running (around 55 ISTR) with the fast road platforms and
junctions at Wembley Park designed for high speed through running as well as
catering for stopping trains.

The maximum runing speed of the Vic Line is around 50mph (47 mph headway, 55
mph trip IITC) - have no details of proposed upgrade.

The maximum running speed of the Central Line in the open air sections is
nominally 100 km/h (109 km/h trip speed) on 10 code. The resignalling had
to achieve a set target for potential round trip run time to ensure payment
of Governmental part of cost so the maximum speed possible was always used.

The restriction on the number of codes and spots available within the sytem
led to a "pseudo" 9 code to achieve 80 km/h on the tunnel stretches east of
Liverpool Street. The target was unattainable without this (8 code was ISTR
64 km/h) and we could only get this speed by a normal code by losing
performance elsewhere on the line at a greater run time penalty The basis
was a triple group of shortish track circuits (just long enough for a 10/8
brake) with the first two normally allowing 10/10 full speed runs but with
coasting applied. The third section was set for a 10/8 brake until the
train was close and proved to be below 80 whereupon the third section was
reset to 10/10. The coasting was switched off at a point which ensured that
the now accelerating train could not exceed the nominal 9 speed and coasting
was switched back on foer the next 3 track block.

In basic terms. The Central & Jubilee lines were the first to be equipped
with "modern" traction packages. The traditional traction packages
typically drew the maximum current just prior to changeover from series to
parallel. It was common to increase the maximum current at this point when
new stock replaced older with the linside section breakers having to be
reset to allow operation of the new stock, yet still protect the old from
short circuit. The introduction of the 1973 stock onto the Piccadilly was
fraught with difficulties if too many new trains ran in a section together!
The modern stock is usually set to draw a gradually increasing power to a
set maximum and then draw that current until maximum speed is attained.
This means that acceleration at speeds above 10 to 15 mph is considerably
enhanced on the modern stock.

--
Peter Corser
Leighton Buzzard, UK






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