On Sat, 29 May 2010 17:57:08 +0100, "Peter Masson"
wrote:

Or do what was done with the DLR, the ever-expanding railway, and design it
so that it can be expanded. Easier to do with a surface railway than
underground


The DLR has certainly proved to be expandable, but I can confirm that
it was never designed with that specifically in mind.

Of course the simple, cheap construction helped, but that was designed
to make it cheap to build, not to make it expandable. That was just a
side effect of the simplicity.