On 15/10/2020 10:47, David Batho wrote:
> Would it be some kind of ‘transponder’ for the tram’s location, or to trigger appropriate announcements in the tram as it approaches the stop?


I think you are right David.

I suspect the thick white discs are new 'signposts' for the AVM (Automatic Vehicle Monitoring) system.

I did a search of Vic tenders and they pur out a tender for an upgrade to the old AVM system, last year.  It included the following line:

*"The AVM uses radio signposts (270 on the network) and odometer to locate trams, which are reported as being the last-reported distance (meters) past last signpost, and is shown to Controllers textually, as well as on character-based line maps. Meanwhile there are 1700 stops on the network, of which the system is not aware."*

So I am assuming these are the new stop based signposts, but I don't know why there are sometimes 1 and sometimes 2 - it could be a roll-out change in progress.

My understanding is that the plan was to go to GPS, but it was found to be unreliable in the Melbourne CBD due to high rise buildings.

Mal Rowe - observing change