A Sydney Morning Herald article has reported that it is being suggested for a number of stations to lose their access to Town Hall, but the Cumberland Line is to be given an upgraded service and run through to Richmond. These changes are sure to be unpopular and reduce the effectiveness of Cityrail, so the question is why would it even be considered? One word: sectorisation. This means that parts of Cityrail can function independently of the whole, as has been all but achieved with the Illawarra and Eastern Suburbs lines. Cityrail branded this concept clearways a number of years back.
Basically, to have a strict sectorisation the Cumberland line would need to either be completely removed, or pushed into what is known as sector 2, meaning lines accessing the City Circle. This means that lines through Parramatta platforms 3 and 4 need to go to sector 2, and given that it is not possible to come from the Richmond line without accessing these lines, the Richmond line needs to go along for that ride. Since trains serving Harris Park, Wentworthville, Toongabbie and Pendle Hill normally only use Parramatta platforms 3 and 4, these trains would no longer be able to reach Central. Similarly, Clyde, Auburn, Lidcombe and Burwood would no longer have a single seat service to Parramatta. Clyde stops would need to be added to selected south line trains. The most popular peak pattern - All to Redfern/Parramatta/Blacktown/Mt Druitt all to Penrith would need to be slowed down significantly with probably 6 more stops. It's not entirely clear why the lower Northern line cannot run through Town Hall with sectorisation however, even with the conflicting move* between outbound interurbans and inbound suburbans north of Strathfield. It is also unclear how Blue Mountains line trains would operate at all if this is done.
This is sectorisation becoming the enemy of Cityrail doing a good job, rather than its friend, which it usually is. I feel this is being leaked now to soften up users of Cityrail for a timetable which isn't going to be liked. It is certainly true that the Western Line needs its own path through the CBD though, which should have been built before the Epping Chatswood Rail Link was.
What alternatives are there for 2013?
Increase running into Sydney Terminal for the Western Line. It is unclear why there are still 3 (both directions combined) Springwood trains per day crossing the Harbour Bridge. This was done before the ECRL freed up a few paths across the Harbour Bridge so there is precedent.
Run additional lower Northern Line trains into Sydney Terminal. This is a satisfactory option for increasing the Northern Line which is incredibly overcrowded but does nothing for the Western Line, which is nearly as bad.
Run all lower northern line trains into Sydney Terminal. The existing trains should not be damaged in this way, even if increased in frequency. Varied stopping patterns cannot reasonably apply for the Western Line between Redfern and Parramatta so all my comments above would apply in that zone and about the Blue Mountains Line trains being virtually unable to run.
Connect the lower Northern line the City Circle, moving some or all of the inbound AM Bankstown line trains to the Museum. This has a conflicting move* at Macdonaldtown and thus would surely reduce reliability to pre-2005 levels so has a snowballs' chance of proceeding.
* A conflicting move is where one train needs to get in the way of a train on another track, blocking its progress. While it can be timetabled, things don't always run to timetabling. It ultimately reduces reliability.
UPDATE 22/6/2012: Or here's a better idea: Terminate the Cumberland line at Parramatta from the south. This means that Parramatta platforms 3 and 4 can become part of sector 2 and Harris Park commuters need to backtrack to Parramatta to reach the CBD. This is not really a big problem as they are likely to have a faster trip to the city by doing this in any event. This means that all tracks and platforms at Westmead and west are available to sector 3 trains without violating sectorisation and it also means Cumberland trains don't run relatively uselessly all the way to Blacktown.