How to realistically mix local and shinkansen on a 4' x 8' layout?

[kvp]

You only need one S72.5 on the diverging route after the turnout to insert the island platform..

Since neither Kato or Tomix produce any curved island platforms with tapering ends, i decided to make the Tomix one look more like the Kato one. On the other hand, you can remove one S72.5 from the left side and one S18.5 on the right to balance it. (add one S18.5 on the inner curve) The fact that you can shift the tracks by half the track distance even at different angles helps. Still, making the platforms narrower or wider won't really modify the maximal train lengths the stations could fit and you can get quite large trains into a rather small layout with both continous running capability and station platform space so the can actually stop somewhere.

 

I think what matters is that on a 240x120 (8 by 4) layout, you can run even the longest japanese trains with prototypical length and you can make a station that is long enough for them. It will be a bit cramped (like many prototypes in Japan) but it's possible, even without resorting to flex track and scratch building everything. If you decide to ditch a connecting line between shinkansen and commuter networks, then you can even go mutiple level without hard inclines and still have the space to add buses/trams in the middle along with yards and either one large station per level or two smaller ones. So people with a 8x4 layout space don't have to limit themselves to having just two loops with little or no turnouts a single station and 5 or 6 car trains.