Apologies for the typo in my original post ( "cocongestion" )!
I don't believe it's stretching it at all (I did say *little* Castlefield). When Virgin introduced the so-called Very High Frequency timetable after the West Coast route modernisation, Morecambe had to lose a peak-time commuter service into Lancaster. I would fully support your sketch for a half-hourly Morecambe service but the conflicts show that there's little to no room for service increase over Carlisle Bridge.
The current headway is 4' though, as opposed to Castlefield's 2.5. Also there is room to play on Lancaster-Carlisle, which there simply isn't on Castlefield. I've had to plan additional traffic on both of them, and I can tell you there's no comparison.
Not a criticism at all, because I'd love to see a half-hourly Morecambe service; but your xx:007 departure from Lancaster would have the xx:07 / xx:08 Birmingham - Scotland treading on its heels (because of the lack of overlap at Lancaster North junction). The return trip would, at xx:29 at Morecambe South Jc be hard on the heels of an up Trans-Pennine but just workable; the xx:37 departure from Lancaster would presumably be constrained to depart from platforms 1 or 2 to avoid a conflict with the arriving, up Avanti at xx:38; and as said above, the return at xx:59 (Morecambe South Jc) would be just after the down London Avanti and also the up Birmingham Avanti have passed (just workable).
So it was done using a RTT train list that I'd selected 'WTT only' on, but of course I'd forgotten that it doesn't put the WTTs that have been amended back in. I've checked a future date and can see the xx.09 departure - the 13.09 does however have (1.5) pathing approaching Oxenholme, so perhaps there's enough slack in that departure to get the diverging margin at Morecambe South jn.
Without a proper graph I couldn't see a resolution for the xx.59 conflict you mention. There may be one but I'm not going to try and plan Preston on RTT.
If you're foolish enough like me, to follow Real Time Trains all day
you'll no doubt see the regular pattern of, e.g. "up" services on time all the way from Scotland but then picking up a few minutes' delay around Morecambe South Junction.
Are there any current TSRs or similar that would be impacting this, they didn't used to have a problem?
In the rail user groups and Community Rail partnerships locally, it is recognised that Carlisle Bridge is congested; it's just Network Rail who don't admit it!
There's a difference between being quite busy and being congested by the definitions as laid out in the Network Code. Although I will concede NR have a habit of trying to desperately avoid declaring congested infrastructure because then they have to come up with a plan to solve it. However AIUI there is a big resignalling programme coming soon that IIRC does include ETCS, and that will have a massive impact on Lancaster-Morecambe-Carnforth area because of the abolition of approach control.
