Tom Anderson wrote:
Anyway, as others have mentioned, all this involves crossing three tracks
on the flat on the way to FP, and two on the way back. Plus, something
that hasn't been mentioned, i think, is that the Canonbury curve is
single-track - the tunnel there isn't high enough to take two full-height
freight trains, so it was converted from two tracks to one in the middle
(where the arch is highest) when it became an important freight link.

If the signalling were being redone, this could be arranged by gauntletting
the track so that there's one tall track down the middle and two short
tracks half-overlapping the wide track:

http://en.wikipedia.org/wiki/Gauntlet_track

That would mean blocking the track in both directions for freight trains...
but that's no different to how it is now.

Gauntletted catenary could be interesting though...

Theo