On 17 Apr, 23:52, Tom Anderson wrote:
You'll see that between Dalston and Highbury & Islington, the NLL-ELLX
route is four track, but paired by destination, with the ELL tracks to the
south of the NLL. Tracks continue to the west of H&I only from the NLL.
That means that, even with crossovers in the right places, trains could
only run from the ELL to the west by making a conflicting movement over
the eastbound NLL track, which, given the frequencies involved, is
basically a no-no. And i'm not even sure there are crossovers in the right
place.

The upshot of this is that the ELL will run only to H&I, which will leave
the ELL and NLL as completely segregated services, maximising their
reliability and potential frequency. Short of throwing in a flyover at
Dalston, there's not really any way to deliver a practical railway other
than this.

The viaduct is wide enough for four tracks all the way to the junction
west of Camden Road Station, where it inexplicably narrows to two
before diverging. If the viaduct was widened here for 500ft or so to
enable the two services to remain separate, you could continue have
totally separate ELL and NLL services; The ELL to Willesden Junction/
Queens Park via Queens Park, and the NLL to Willesden Junction via
Hampstead.