The Marulan sector consists of about half existing alignment and half new alignment around Uringalla. The country is undulating, meaning that significant earthworks and possibly some tunnelling and structures may be required.
This sector involves some difficult terrain, with the Wollondilly River winding between hilly country. The eastern part of the alignment approaching Marulan is unproblematic; curves are minimal and there is even a former trackbed on the north side of the tracks that can be reutilised for most of the length.
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.