One of the difficulties designers must wrestle with is that on average people walk at about 1.4 Metres/second and at that speed it takes 4 minutes 45 seconds to walk the length of a 400 Metre train. There will always be slow walkers, so in round terms, at least 5 minutes must be allowed. That makes it unworkable to clear the platform of incoming passengers before allowing outgoing passengers onto the platform. So one of HS2’s designs is to hold their waiting passengers in waiting rooms above the platforms. But they also separate their passengers by destination. HS2’s design has 3 tph to Birmingham (so space must be found for 20 minute’s worth of passengers) but the þ-shaped route has a train to Birmingham (and beyond) every 6 minutes.
So I propose a 4 track station, with a platform between tracks 1 &2 for all trains going west of the Pennines, a platform between tracks 2 &3 for people going to Scotland and the North - East and a platform between tracks 3 & 4 for people going to places on the east side of the Pennines
This is workable. Trains will be coming in from the North every 3 minutes, they will rotate around the platforms giving a train 12 minutes to come in, incoming passengers to get out and outgoing passengers to get in. It seems very generous when you look at HS2's plans of 2 working platforms each way and a spare a side at Old Oak Common. Shinkansen trains stand in Tokyo station for 13 minutes before going back out again.
It will need a travellator from Euston Rd to the north end of the platforms, passengers will need to pass through the ticketing barriers before getting onto the travellator or else there be no ticketing barriers at all; the tickets being checked elsewhere. It will also need well-presented information.