A flyover at the city end of Sunshine station feeding into platforms sorted by their final destination is the most logical arrangement given the lack of space for junctions at the other end.

Yet Melbourne Airport Rail is jamming in a flyover at the down end because they don’t want to rebuild Albion or Sunshine stations, because “it appropriately allocates relevant project costs to MAR”.

https://twitter.com/aussiewongm/status/1572369864463126530

The proposed upgrade to Sunshine station is yet again going to constrain future capacity by cutting costs now, if the plans that have been publicly released are anything to go by. What they should be doing is expanding the station to four island platforms of 250 m length (with space to accommodate future extensions to 400 m), allocating two platforms to V/line and two to Metro, and building a set of flying junctions on the Up side to eliminate route conflicts. If the platforms were arranged so that 1,2,5,6 were allocated to V/line services and 3,4,7,8 were allocated to Metro services, this paves the way for complete separation of the two operators once an extra track pair is built along both the Ballarat and Bendigo branches. It would also remove an impediment to standardising V/line.

The flying junctions needn’t be as elaborate as the ones in Sydney that sort suburban services. One flyover that has three tracks at the Down end and bifuricates into a single track and a pair of tracks at the Up end will do the job. The Up Sunbury/Airport line would pass over the Wyndham Vale lines, and the Bendigo lines would pass over both the Wyndham Vale lines and Down Ballarat line.

Why doesn’t DoT, V/line, Metro, or indeed anyone plan for incremental future upgrades by doing it right the first time?

Yep – started with the new timetable on 30 May 2022, they currently run express through Sunshine to just Tarneit and Wyndham Vale thanks to the short platforms.

Back in 2016 the State Government allocated $5 million to investigate the Upfield – Somerton link:

https://www.premier.vic.gov.au/getting-it-done-for-north-east-victoria/

Peak hour suburban services get horribly crowded and besides possibly putting in an extra platform at Craigieburn I’m not sure you’d get more V/Line services in. Maybe they could use the broad gauge track on the Albion Jacana line but they need to reinstate the Somerton link ASAP