I suspect that the Eltham railway trestle bridge is on a historic register, and having once lived in the area both the previous and current Council are very well aware just how hostile the locals are to removing the bridge.
The problem is the bridge is expensive to maintain as it has deteriorated despite constant maintenance. When a train goes over, the bridge gently sways ! So at some point radical surgery will be required. Despite appearances, the under deck is actually supported on steel girders inserted about 30 years ago ( Does someone here have a more precise date ? )
The ETRB actually does have a skilled crew who are able to repair and replace these timber trestles , and they have done work in the past for VicRoads. Some years back there was an article in PBPS' Narrow Gauge which illustrated the use of reinforced concrete foundation, upon which stirrups were embedded to hold the timber trestle bridge. This protected the timber from water rot and yet retained a genuine timber trestle bridge. The fact that timber trestle bridges in Australia generally lasted for 70 + years indicates that this was, and in some cases still is, a viable engineering alternative.
One solution that I have heard suggested is to transfer the wooden trestle bridge to the down side of Eltham and use it as an extension of the dual walking and bicycle track, which would allow for a concrete pylon double track railway bridge to be built on the alignment , and that way save the footy oval from being destroyed by the Liberal Party proposal to build a dual track concrete pylon bridge on the down side of the existing timber trestle bridge.
( I am surprised that Mathew Guy, as a local, does not recognise the Hornet's Nest destroying a heavily used footy oval will cause. The footy oval is well used 7 days a week, and the idea of cutting a large swathe of it away is political suicide. )
I agree with"justarider" that the line need not be duplicated beyond Wattle Glen, as a future increased frequency would meet current and future demand for quite some time. From a Passenger numbers perspective, terminating some services at either Eltham or Diamond Creek so that only every second train goes to Hurstbridge may be an option to consider.
The reference to the construction of an island platform in lieu of the existing Platform 1 , so that Up Epping and Up Eltham trains could arrive in parallel is actually quite sound, and the VR & Connex both did consider that when Clifton Hill underwent the two upgrades , but funding was not available to do so. At the time the thinking was that passengers could do a train change during the morning peak , and after 730pm /1930 all trains would just use the island platform. I acknowledge that it is tight under the road overbridge, but as it is all railway land between the pylons, this was a possibility.
Looking at it in todays terms , I suspect any rethink of this arrangement would probably make allowance for longer trains and the removal of Ramsden St level crossing. Longer trains are an option, and unfortunately, Double Deck trains are not, partially because Victoria's Metropolitan Loading Gauge is lower than NSW , and both Metro and PTV ( or whatever it is called this week ) are not in favour of Double Deck trains full stop.
The other problem with longer trains are Collingwood / Victoria Park and West Richmond / North Richmond stations. In the case of Collingwood / Victoria Park the solution might be to extend Collingwood in the down direction , build a pedestrian bridge to cross Johnson St and close Victoria Park station. The distance between Collingwood and Victoria park stations is just over a six car train length.
In relation to West Richmond / North Richmond, the solution might be to extend North Richmond in the up direction, and build a pedestrian bridge towards West Richmond station and close West Richmond , which from a passenger ( ok , customer ) safety perspective , leaves a lot to be desired , and has been problematic from a safety perspective for. very long time.