For the cost of building a duplicated bridge over a single track bridge, go build yourself 10-20km of improve aligned track someone else and save even more time as due to the proximity of the bridge to the yard, all trains would already be starting to slow as they cross the bridge if they were at speeds exceeding 100km/hr.There is going to be a significant issue with rail capacity between Junee and Melbourne that DS will not help but actually hinder.Curious to know how Double Stacking would reduce capacity?
They are slower because they are heavier. Dual track allows trains to maintain a higher average speed due to not having to stop in loops for oncoming traffic. Average speed is more important between Sydney and Melbourne because there is not just freight but also passenger trains from both nsw trainlink and vline along this corridor.
The menangle bridge was life expired and it was upgraded. As was the historic viaduct at shepherd street in Liverpool and across Cabramatta creek at warwick farm.
Single track operation commences 2km north of Albury station if it was DT to Albury station which has crossing loop, finishing just south of the station headed south so duplicating the track from the Vic side of the river 2.5km to the station is for the benefit really just the V/line trains because north of here its same same for a few hundred km. If a cross is required for XPT or V/line, they will just wait it out at the station, total time about 1-2min, in the very rare occurrence this is. Not ideal but money could be used elsewhere to speed things up more. You would need cross overs anyway to bring V/line and XPT into their platform roads and/or by-pass the freighter around them.
You are not arguing to retain the current structure and allow twin track operation because the current bridge is F__ked and will need replacing anyway at some stage sooner rather than later and likely to have a great impediment on traffic speed than DS.
The Menagle bridge is a short non-timber structure.
The Albury bridge itself could probably be saved with lifting the cross beams to DS height, but there is an extensive lead up of timber structure either side and this needs to be removed and does not belong on a modern railway and is not the same as your quotes above. If the bridge girder and supports are still questionable, remove the structure and place it somewhere where it can be appreciated or donate to a H&T railway and not on the mainline railway.