In the 1950's I lived in North Harrow and think the Met had only two
tracks
running between Harrow on the Hill and Moor Park and beyond. A recent
photo
shows a second set of lines on the south west side of the station.

That could of course have been the BR (ex-GCR) lines. South of and
including
Harrow-on-the-Hill they are on the south-western side of the formation,
giving Harrow three island platforms (from south to north Marylebone
down/up, Met down and Met up). I can't remember whether this arrangement
continues north of Harrow Junction.

As far as I've been able to gather from various sources, Harrow-On-The-Hill
has always been the point where, heading south, the GC and Met parted ways.
In "Great Central Railway's London Extension" by Robert Robotham, two
different track plans are given for Harrow-On-The-Hill:

The first shows harrow as having two side platforms and one island platform,
with four tracks. To the south-east, the two northern tracks were the Met
line to Baker Street, and the two southern ones were the GC to Marylebone.
However, the trackwork allowed any Met train from the south to access all
but the most northern platform, and vice versa that any Met train from the
north could access all but the southermost platform. The GC, however, could
only use the two most southern platforms when arriving from Marylebone, and
so consequently would have to use them when approaching from the north too.
The Met lines as far as Harrow-on-the-Hill were quadrupled in 1932

Heading north-west from the station, the four track converged to 2, shortly
before diverging again into 4 - the northern tracks heading to
Rickmansworth, the other two being the Met branch to Rayners Lane /
Uxbridge. This was obviously a huge bottleneck, and in 1936 a dive-under was
put in to remove conflicts.

In the early 1960s, however, the Met lines were quadrupled further north
from Harrow-on-the-Hill, and separated from the GC lines (the new track-plan
showing only one physical connection between the two). From the south, the
arrangement is simple enough - two up lines to Baker street, two down lines
from Baker street, then Marylebone up/down.

The Met lines had scissors at the southern end of the station to allow
trains from either Rick'wth or Uxbridge to access either of the fast or slow
lines, however switching from the down direction to the up direction was
possible only by a) a head-shunt fitted in the centre of the four tracks,
north of the station, or a trailing cross-over between the middle two
tracks, which were for Uxbridge (see below).

Heading north-west from Harrow, the two GC lines remain at the south side,
but on the met, the outer-most two lines go to Rick'wth, whilst the inner
two lines served Uxbridge. The dive-under then took the two GC tracks and
the down Rick'wth line of the Met over the two Uxbridge tracks, giving (from
north-east) Met Rickw'th up/down, GC up/down, Met Uxbridge up/down.

Presumably, the four tracks heading towards Rickmansworth pair off to two
tracks after Moor Park (which was completely rebuilt when the GC/Met was
quadded) / Croxleyhall Junction (or what I call "the Watford triangle", to
rhyme with "Bermuda" ;-P).

Not sure if the reference to "second pair" of lines is
strictly correct. Certainly the Met south of Harrow is paired by direction
(very efficient use of space, with the slows in the middle, because you can
use a single island platform where there are no fast platforms, as at
Northwick Park for instance, and one island for each direction where fast
trains stop, Harrow for instance).

Most definitely a good arrangement. Had full-scale quadrupling of the GCR
occured, this is the model they intended to use. Fast on the outside, slow
on the inside, local stations therefore needing just a single island
platform. You can't get simpler than that, can you?

This pairing by direction does not appear to continue north of Harrow,
judging by the track-plans I have. It merely separated the GC and Met lines.
However, more recent works may have changed this arrangment.

Mayn alopogies for the inevitable millions of spelling / grammar mistakes
which may have rendered this posting unintelligible, but my brain is running
on empty at the moment, demanding sleep urgently!

Ronnie
--
http://www.blugman.freeserve.co.uk

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