"MIG" wrote in message



Original train formation/length doesn't seem to stop 1972 stock being
compatible with 1967 stock or 1992 stock running on the Waterloo &
City. Units can be reformed.

Not so easily with complex new stock. The W&C and Central were
re-equipped at the same time with essentially identical trains, except
that the W&C trains had only one pair of the two-car units. The W&C line
was re-built at the same time.

The 1972 stock is based on the 1967 stock, so they're very similar (but
with different cabs, of course). Similarly, the 1995 and 1996 stocks
are close cousins, but aren't electrically compatible.

But the new 2009 stock is being supplied in fixed 4-car formations that
wouldn't be easily re-formed. Its 8-car trains wouldn't fit any other
tube line.

Of course, things are going the other way on the SSL, with, for the
first time ever, the same stock used throughout with the new S stock.