Diverting railways into tunnels is an idea that comes up from time to time. It has been proposed in Edinburgh before, with a railway running in a tunnel under the southside. That proposal was to replace the current railway through Princes Street Gardens. Now a tunnel has been proposed again, by experts Richard Rooley and Terry Wyatt, with an underground Waverley Station. But is this a feasible option? Waverley Station already has a basement level - this is below the eastern two-thirds of the station - and the platform-level buildings are supported on this basement, as are the platforms themselves.
