The geography between Moss Vale and Mittagong presents a significant barrier to infrastructure development, both due to the built up areas of Bowral and Mittagong and also the imposing topography of Mt Gibraltar. For this reason, re-use of the existing corridor is the best and probably only option here.
Now we are really getting into the heart of the Southern Highlands, with its beautiful rolling pastures, cute hamlets, manicured golf courses, and of course the Shoalhaven Escarpment on the southeastern side. The existing railway between Bundanoon and Moss Vale is pretty windy, so we will need to build a completely new track through moderately difficult terrain.
The existing alignment out of Goulburn has a minimum radius of 600m, yet it should be possible to increase to 1000m or possibly 1500m with only small modifications to the existing corridor. Geography, other transport corridors and existing development impose substantial constraints beyond this; any faster deviation will be very expensive and should therefore be deferred until higher-speed operations are required.