Secret Rail plans part 3: Airport line stations lose out from East Hills overcrowding

Several blogs have speculated on the future of the Airport line, including this blog's thoughts on connecting to SRT and also Transport Sydney's similar analysis.  There is a lot of logic to connecting the Airport line to the SRT, but how does this reconcile with TfNSW's "secret rail plans" to run the Airport line instead as a shuttle to Central?  Which will it be... a shuttle to Central or a branch of SRT?  [However, for alternate views on why the Airport line should not be a branch of SRT and not also terminate at Central see this post.]

First a bit of historical background.  The Airport line was constructed in the 1990's and currently operates as a "detour" off the East Hills line, that offers an alternative route for East Hills trains to enter the city circle from the South.  Stations on this "detour" consists of Wolli creek, Domestic, International, Mascot and Green Square stations  (which I will collectively refer to as "airport stations").   As shown in the overcrowing diagram below, they are predicted to be some of the most congested parts of the entire Sydney Trains network:

At Central station, the Airport line trains use platforms 21 & 23, and so are kept separate from the other East Hills line trains, which use platforms 20 & 22. After Central station, these trains converge and traverse the city circle anti-clockwise, and come out to the west as the Inner West line trains (the green route in the diagram below).

Close analysis of TfNSW's internal 2019 patronage forecast document suggests to me the Airport line will be a shuttle prior to construction of SRT, and this then further strengthens the logic of connecting it to the SRT longer in the longer term.  The clue comes from Figure 10 of the patronage forecast documents, showing patronage for the East Hills and Airport line:

Yep, that's right... the patronage forecasts for the East Hills & Airport line does not show any boardings for the airport stations, which are meant to be the most overcrowded parts of the train network.  In fact, they are left off the forecasts altogether.  Surely this must be an oversight or a mistake?  Nope, more likely deliberately left off as the East Hills line will be at 130% seat capacity at Turrella ie: prior to Wolli Creek... adding the airport stations from Wolli Creek to Green Square into the above forecasts would have the East hills line skyrocketing to 150%+, even 170%+ seat capacity of the line.

Maybe there will be additional airport services that weren't shown in Figure 10?  Nope.  Not if these additional services are to run through the city circle (like current East Hills & Airport line services).  Note that Figure 10 of the TfNSW patronage document shows 16 trains per hour on the East Hills line excluding airport station services, and these trains are already full west of the airport stations.  Is there anymore capacity to include additional services for the airport stations?  The city circle can handle 20 trains per hour in each direction.  However, in the 2019-2020's period (prior to construction of SRT), the Bankstown line shares city circle capacity with the East Hills, Airport and South/Inner west lines.  Note that the Figure 11 (below) of the TfNSW patronage document shows plans to schedule 10 trains per hour for the Bankstown line, and this fits neatly into the 4 spare slots left by the East Hills line's 16 trains per hour and the 6 spare slots left by the South/Inner west line's 14 trains per hour.

So the bottom line: no spare city circle capacity for airport station trains - they are the "losers" in the 2019 TfNSW plans.  Ok, so without the ability to channel airport station trains into the city circle, what will happen to them?  The leaked "secret rail plans" had a plan of the airport line to run as a shuttle terminating at Central, where a "new platform" would allow easy interchange for a continued journey into the city.  So in the period prior to construction of SRT, what will comprise this "new platform" and which rail service will airport station passengers then interchange onto, given all other rail lines will also be at capacity?  Well, as shown below, the airport line platform at Central is right next to the CBD light rail Chalmers Street platform... it looks like Clover Moore is going to get her beloved Green Square "light" rail - except not in the form she thought she was going to get it!  (For clarity, I am not suggesting Airport line will be converted to light rail).

So why is TfNSW planning this convoluted change for airport station services?  The rail overcrowding diagram at the top showed why... the East Hills line is the most critically overcrowded, and it's capacity can't go any higher than 16 trains per hour prior to SRT.  Attempting to squeeze all the passengers boarding from the massive high rise developments at Wolli Creek, Mascot and Green Square onto trains that are already at 130% seat capacity prior to Wolli Creek is going to cause chaos.  So the answer is that the East Hills trains will run express from Turrella into the city circle, and bypass the airport stations altogether.  All of this makes me wonder though, why does the Department of Planning want to add even more housing on East Hills line stations beyond Glenfield?  Looks like the left hand of TfNSW does not talk to the right hand of Planning!