"D7666" wrote

Again this is why I think the existing TL route is and always be a
slow speed metro route thus is better off being a sort of overground
route.

24 TPH yes, attempting to serve most of the south coast and deepest
fenlands no.

I understand the point you and MIG are making, but the opportunity to run
that sort of Thameslink as probably lost in 1916, when the original high
frequency (for those days) inner suburban to inner suburban service via the
Widened Lines collapsed (as much as anything because the paths were needed
for freight).

North of the River, Thameslink now serves a medium-distance operation along
the MML (north of Kentish Town there are only 5 stations out to the boundary
of Zone 6), with City Thameslink almost exactly half way between Bedford an
Brighton. On the new Great Northern route, the shorter distance routes to
Welwyn and Hertford are served from Moorgate via the Northern City Line;
it's not possible to lengthen trains to Moorgate beyond 6 coaches, so
Moorgate is no use as a terminus for the longer distance GN commuter trains
to Cambridge and Peterborough. So these will have to be served from
Thameslink and/or Kings Cross. And again, Cambridge and Huntingdon are very
little further from London than Bedford or Brighton.

South of the River, Thameslink designs mean that the main routes which can
be served are the London Bridge - East Croydon fast lines, with a more
limited service on the SEML, and via Elephant & Castle. But to avoid
conflicts south of Blackfriars, the Blackfriars bays are moving to the west
side, so will serve the Herne Hill route, while Thameslink will serve the
Catford Loop, which only has a limited inner suburban passenger potential.
On the Croydon corridor, the slow lines are being connected up to the ELL;
it is desirable to keep ELL and Thameslink trains as separate as possible.

So future Thameslink must be thought of mainly as a Bedford, Luton,
Huntingdon, Cambridge and Stevenage to Maidstone, Tonbridge, Brighton, etc
railway, with 5 central London stations (St Pancras, Farringdon, City
Thameslink, Blackfriars, and London Bridge). It's a bonus that it also acts
as a metro between these five stations, where it will give considerable
relief especially to the City branch of the Northern Line.

Peter