How much would it cost to re-align the main south route to follow the Hume Freeway from Yass to Albury? There would be no cost for buying the land because the freeway reservation is wide enough, and it should cut several hours off the Sydney-Melbourne trip, especially if it goes double-track all the way. The curves will be a lot gentler, the grades shouldn't be much of a problem, and the distance will be shorter.
It will skip Junee and Wagga, so the old route will have to stay too - also as an emergency route if the main one has to be closed for whatever reason.
If it was double-track all the way to Albury, that would be an additional influence on the Vic government to duplicate the SG line from Melbourne to Albury. At the moment there's hardly any point because of the single track Albury-Junee section.
While a rail line along the Hume Highway is significantly shorter than the route via Harden, it goes through much rougher terrain, even with 1 in 40 grades. That's the reason the rail line went via Harden in the first place. A short cut also suffers from a big disadvantage in that it has to be built all in one go to be of any value. That's the reason why the Alice Springs to Darwin Railway was so difficult to get off the ground. Alice Springs to only say Pine Creek would be worthless. Surly much better to upgrade the existing roundabout line via Harden than try the Hume cutoff, which is far too ambitious at this stage. I am happy to listen to evidence that the grades along the Hume Highway are fine for rail.
At the moment there's hardly any point (in duplicating Melbourne to Albury) because of the single track Albury-Junee section.
I fundamentally disagree with this statement. Any increase in the amount of duplication, whether exension of crossing loops, extra loops, or proper duplication will tend to reduce delays at crossing loops. The main thing is to spead the extra second track out over the whole Junee-Melbourne section so that adjusted for train numbers, the length timewise of the remaining single line sections are reasonably even. The existing single line sections are severely imbalanced in length. A beautiful advantage of this work is that it can be done in dribs and drabs.
Regarding the existing 900m loops that are too short for 1500m trains, the amount of track required to bring them up to size is quite small. If say 20 short loops between Junee and Melbourne need to be extended from 900m to 1500m that takes "only" 600mx20=12km of track. The lack of such a small amount of track causes long 1500m freight trains to sit back one or two loops away from the ideal crossing loop, 30-40-50km away and 30-40-50 minutes away, wasting hours and hours and hours. The stupidity of this situation beggars belief
. The beancounters are however completely happy, since they are focussed on big glamourous projects, and crossing loop extensions are as glamourous as ... ... colostomy bags.