In the late 1980s while working for Australia Post, I was given photos from a retiring member of staff that were otherwise destined for the rubbish bin as, by that stage, AP had dispensed with the services of their State historians.

Among the photos was the one above showing an experimental monorail. All that I could determine was the intent/thought was that a monorail train could run through the services tunell under Little Bourke Street (used for water/power/phone). Little Bourke Street had abutting it the side entrances to the Melbourne Mail Exchange (Spencer Street) and the GPO (Elizabeth Street) which housed the City Delivery Centre. The concept was to carry the mail between these points - less than 1km apart) rather than transport by truck.

Why the concept was not pursued is not known. Possibly it may have come unstick as the tunnel was owned by the Council, not Australia Post, and used by other bodies to service all the buildings in the area.

Another item that did use the city tunnel system in the pre WWII era was a pnuematic tube system linking the Mail Excgange (which was in its early days the Melbourne GPO for many years) and the Stock Exchange.