Re: [NSW] Strange rails at Hurstville

[Graham Fry <fryg@sydpcug.org.au>]

I am not sure whether this explanation now applies. In the past when the
city underground was built the additional rails were placed in position
between the running tracks and electrically bonded to them. Their
purpose was to reduce the electrical resistance for the return current
from the train back to the supply substation. It was thought that
without these extra rail the return current would find alternative
parallel paths such as pipelines which would lead to rapid corrosion of
the pipe. 
I don't know whether this theory is still accepted but it might have
some validity in that these extra rails are where buildings are built
over rail and without the extra earth return the building's electrical
system could be affected by the traction system.

Graham Fry