A link at Waterloo itself could be fairly easy it has to be said, but it's the rather dismissive mention of 'flyovers between Battersea and Waterloo' that reveals a lack of thought as to which services would actually be joined across such a link. Thameslink via London Bridge worked as a concept because from a very early stage planners had a very good idea of which services had to cross over which others and, whilst precise details might have changed over the years of development and deferment, the basic forms of the Borough Market widening and Bermondsey grade separation were understood right from day one. I see no such detailed consideration in the Southern Cross proposal. Also the proposal makes reference to local services out to Dartford and Sevenoaks, but mention of longer distance Kent services currently using Charing Cross is notable by it's absence. They'd have to go somewhere else seeing as Charing Cross would close, and where exactly in the South Western local network they would terminate is not considered at all. To me, bolting South Western and South Eastern long distance services across the link would seem to be a recipe for poor performance right across the network and should be avoided at all costs. Capacity of 160 trains an hour is also mentioned, a greatly overstated figure. Even at proposed Thameslink core capacity no more than 96 an hour would be possible in total over the four tracks (I assume) proposed, and there's no room to widen the formation through Southwark without major demolition. Not least of the challenges for this scheme would be the four track section through Southwark including the recent Thameslink widening over Borough Market, where existing Charing Cross services will run over a dedicated pair alongside another dedicated Thameslink pair. So even with four tracks, if Southern Cross was to co-exist with Thameslink (via London Bridge) then this section would need to be widened again to six tracks - can't see that being popular with the locals so soon after recent and ongoing works. Thameslink is a clever scheme where a modest intervention could deliver transformational benefits, yet without tearing up the entire historical South Eastern service pattern. Whilst superficially Southern Cross seems a similar relatively small scheme, the ramification across the entire South Western and South Eastern networks make it much bigger than its promoters realise, both from infrastructure engineering and operational perspectives. As such any benefits it might achieve have to be weighed against vary much larger costs and difficulties than assumed.
