I'll catch up with the history first.
How feasible would it be to reopen the link to Huntingdon? Either based on the old route or via the East-West rail route?
The old route is completely infeasible. As already stated, Cambridge North-St Ives is a guided busway. St Ives-Huntingdon closed to passengers in 1959 and has almost completely disappeared. It never saw diesel traction, apart from shunters, and steam traction was class 2s. It had (I think?) 4 bridges over the River Ouse, including some made of matchsticks.
East West Rail faces the wrong way at Tempsford and would need grade separation, for which there is no space.
You had the Donny trains over the joint until March - Spalding was closed. Nether frequent nor fast but it was there.
Only between 1973 and 1982, when it was much quicker to change to/from ECML trains at Stevenage or Peterborough. Prior to that, all the daily Joint Line trains were to or from Norwich, Yarmouth and Lowestoft, apart from the North Country Continental. Cambridge passengers changed at Ely or March. The nearest Cambridge got to a through train to/from "the north" was a summer Saturday Manchester running as a relief to the boat train.
Both Liverpool-Norwich and Birmingham-Stansted are very much tail wagging dog services, where a comparatively very small number of people making long journeys are stifling the provision of much-needed local connections.
I couldn't have put it better myself!
Whenever existing service levels are silly little trains with well below Tube levels of crowding, any statement with 'huge unserved demand' in it probably needs to be put under the microscope.
I have watched the peak hour trains at Cambridge. They are full. The Cambridge-Peterborough trains are well loaded for most of the day.
Can any more services go there without two tracks through the tunnel?
The main constraint at Stansted is platforms, which make it difficult to run longer trains.
Yes, this was a folly when planned/constructed but I suppose nobody could’ve predicted how busy Stansted Airport would become. I recall passing a big sign close to the railway proclaming ‘WHITE ELEPHANT’ in those early days which was matched by the exceptionally poor loadings on those 322s.
For quite a few years the North Curve only had a parly service.
if Peterborough - Norwich requiring a change in a hypothetical future won't be a big deal
could the Ipswich 2-hourly also not cross and turn at Ely
It is important to remember that Norwich and Ipswich passengers interchange with the ECML at Peterborough too. That's why neither Norwich or Ipswich want to lose their through trains to Peterborough.
Whenever existing service levels are silly little trains
I agree on the very small silly trains part, they should be much longer before any infrastructure works.
This is my starting position too. And until now it has been impossible to do anything about it because the silly little trains were run by three separate operators, each with their own different traction, driver route knowledge, and train paths to protect.
In my view the first step is to give all of the services to Greater Anglia, and GBR creates that opportunity. I think that can only be done with the EMR service by splitting at Nottingham, but the XC service could possibly still run through to Birmingham.
Once that's done, Greater Anglia can use some creativity to make better use of the existing train paths. The peak time additional trains at Cambridge with Norwich and Ipswich, that were introduced in May, show that things can be done where the will is there. Greater Anglia have that will, EMR and XC know little and care less about what goes on east of Peterborough.
One disadvantage of the Origin and Destination Matrix data is that it has no directionality. But, anecdotally, I think that we are now in the position that the Norwich and Ipswich flows are dominated by Anglians wanting to get out, but the Cambridge and Stansted flows are dominated by outsiders wanting to get in.
So I would look at whether it would be feasible to do something like this. In the morning peak the eastbound trains to Norwich would run via a reversal in the north end bays at Cambridge. In the evening peak the westbound services from Norwich would run via a reversal in the north end bays at Cambridge. In each case they would take the path of the train an hour behind when they got back to Ely. The last morning train into Cambridge would terminate, because, if it went back to Ely, it would want the same path as the first train going direct to Norwich. Having sat at Cambridge all day, it would then form a westbound train starting at Cambridge, taking the path forward from Ely left free by the first afternoon train to go via Cambridge. None of this would need any more paths between Ely and Peterborough, though it would need more paths between Ely and Cambridge. For Norwich/Peterborough journeys diverted via Cambridge there would still be the option of getting no addition to journey time by changing at Ely.
I think this would probably have to start with a fleet of class 170s. As regular readers may know, I do see Stansted-Nottingham as an excellent route for battery bimodes, though that would need a more radical timetable change.