"Tom Anderson" wrote

The four tracks between H&I and Camden Road are a bit of a mess.
Basically, there are two electrified passenger tracks, and two
non-electrified freight tracks, paired by direction. Except that the
western end of the westbound freight track is electrified and used to
reverse passenger trains, and freight runs over the western end of the
westbound passenger track.

I suppose really, you should think of it as the passenger/freight pairs
merging - the eastbound at the left of the diagram, the westbound where
the crossover from the freight aka reversible to the passenger line is -
and the bay platform being a stub off the merged line. If that makes any
sense.

Also, why is eastbound down and westbound up? Surely when the line ran to
Broad Street, it was the other way round? I can't immediately think of any
lines the NLL interacts with where a transfer of directionality could
result in this situation.

It's a bit of a mess now, with two passenger lines with third rail DC
electrification and a single reversible freight line with AC OHLE. After the
alterations, between Highbury & Islington and Camden Road (both exclusive)
there'll be four tracks, all electrified with AC OHLE, though one of them
will be reversible, but mainly used for stock transfers.

The diagram suggests that there will be 8 NLL trains per hour from
Stratford, of which 2 will reverse in the Camden Road bay, 4 will continue
via Gospel Oak, and 2 will just vanish.

As for up/down, it seems that control is being transferred to Upminster
IECC, and directions will be consistent with what applies there.

Peter