<amoglesm> wrote in message
news:56ee2957-8218-4784-a0c5-d71390b1211e@z66g2000hsc..com...
>
> I would be inclined to say it depends on the relative length of the
> line.
>
> If for example, the length of quadruple track is relatively short, and
> it ends in a terminus, trains coming in on the slow lines will most
> likely go out on the slow lines, and ditto for fast lines, so grouping
> by speed helps reduce on conflicting movement and so boosts the
> overall throughput of the layout.
>
> Sorting by direction makes more sense for longer lines, however, as
> the switching of trains between fast and slow lines can be acheived
> without having to cross other lines. Again, this has repercussions on
> line capacity and service punctuality.
On the SWML the practical advantages of pairing by direction allows semi
fast trains to cross easily to the slow (platform) lines for station calls,
limited stop trains can run partially on the fast lines, and slow trains can
be repathed fast line to make up time and overtake if running late.
Of course the LSWR provided a flyover at nearly every junction as well, the
most obvious problem being the lack of a flyover at Woking, the flat
junction there apparently constrains the whole mainline timetable.
Not so good for line closures for maintenance though.
Paul