We are often concerned about threading out model tracks around each other.  However, the prototype was very good at it.  Here are two pictures, rural and urban, that show how it’s done.

Midford, Somerset.  The Somerset and Dorset viaduct was built and is to the left.  The Great Western built one of it’s last branches underneath, threading the line over the road, the over the disused Somersetshire Coal Canal (the arch still standing)  and under the Midford viaduct.  Clearances must have been tight!

This tiny clip from the start of the Titfield Thunderbolt film shows trains on both lines – including a Wisbech and Upwell tram coach that has seemingly emigrated westwards.

Meanwhile, in London, near Brixton two suburban lines cross the road.  It’s a low bridge, and there can’t be much spare room between the rail lines.

Hope these give you some ideas, or at least an excuse, for your layout.