Is there any chance that the bridge on the original alinement (of the original bridge) over the Hawkesbury River could be reinstated (with a refurbishment of the old piers/pylons and tunnel)
One of the Northern piers failed didn't It ? forcing the replacement of the bridge with the current one ?
Consider how deep the piers have to go, and considering the development of new type of bridge such as the Anzac Cable Stayed Bridge, maybe the Hawkesbury River should be spanned in a single span?
According to Sydway, the river is about 1km wide where the existing bridge, especially if the new bridge is at an angle to avoid sharp curves at the northern end.
It might also be a good idea for a new bridge deck to be higher than the existing bridge deck, firstly to reduce the gradient a bid, secondly to allow for flyovers over the existing track, and thirdly so that any long tunnel on the northern side can be replaced by a series of short tunnels (rather like the 10 Zig Zag tunnels near Lithgow).
Expect such a bridge to cost $1bn.