No-one else seems to have picked this up so here goes...
Why aren't the nice shiny new Class 717 trains running on the Great Northern line yet? Why are they sitting on the sidings in Ferme Park and we're all still clunkily riding on the oldest trains in Britain?? Because yet another time a design blunder has "emerged". This time it's the cabs - the layout dangerously blocks the drivers' view of some signals on the line.
What a way to run etc..
Interesting, they have been in test for months...and I was still waiting to see one in service. Massively disappointing such a fundamental 'flaw' in design stage. Why just these stations though?
Presumably the restricted space for the signals in the tunnels
Speculating as I'm not privy to the info, but the old 313s (and most older BR era units) sit the driver right up against the window with a small control desk.
In the world of advanced tech (requiring space for processing power) and crumple zones and so forth, drivers are finding themselves further back from the end of the train...
As Straw Cat rightly points out, the majority of signals in the tunnels are akin to tube signals, miniature lights mounted down low on the left or right. With a larger bulkhead and the driver sat further back it's no surprise they can't see...
And not an easy fix either.
From what I have read in the extensive discussion of the 717 over on RailUkforums that is correct. There are also passenger sighting issues where the platform is to the right of the cab. See more here - I recommend reading from about page 51 to get a good idea of the issues. Many of those commenting are current and former GNR and Network Rail employees.
Automate the whole fleet, problem solved.