Hi folks, so in my recent video on Melbourne's City Loop, I briefly mentioned the impressive
flyovers at Central station in Sydney, and a few people asked if I could do an explainer on that.
I'll be the first to admit I didn't actually fully understand it myself, but after going over some
maps and diagrams I think I've got it worked out, so here we go! Central station is located
on the southern side of Sydney's CBD, and is the heart of the New South Wales railway system. The
station is effectively divided into two halves – Platforms 1 to 15 are terminating platforms,
used by intercity, regional and interstate trains. This area is known as Sydney Terminal in
some official circumstances, and is often called that by more pedantic rail workers and railfans –
but to the public, it's all Central. Then over here we have platforms 16 to 23,
which are the suburban platforms. They cater for a number of suburban lines coming in from the south
and west, which then continue north into the city underground. The flyover in question, also known
as the Flying Junctions, is located to the south of the suburban platforms just here. It's quite
hard to work out exactly what's going on here just by looking at it, but it's actually a very simple,
and very clever piece of infrastructure. It opened in 1926 as part of Sydney's original
electrification program, which also involved the construction of the first part of the underground.
So the basic principle of the flying junctions, is that every Up train (Up being toward Central) runs
over the top, while every Down train (away from Central) runs underneath. There are some official
diagrams online which I will put a link to down below, but I've decided to make my own for this
video. So this is the approximate shape of the actual flyover structure, with the shaded grey
area being the elevated bit. Over here on the right we have Central platforms 16 through 23.
Now I hate maps that don't face north, but I didn't have much choice here to fit the aspect
ratio, so north is roughly on the right hand side of your screen. Aand here is all the track! Got
that memorised? Good. Ok, so here in blue I'm showing all the Up lines, that is the inbound
lines running over the top of the flyover. So you can see we have five lines coming in from the
suburbs, condensing into four platforms. You will notice that the four lines coming onto the left of
your screen are able to run through the crossovers on the flyover to access any of the four
Up platforms at Central. The only line which can't access all platforms is the Airport line (that's
the one coming in from the bottom of the screen), which can only get to platforms 20 and 21.
Now if we look at the Down lines shown here in red – so these are the outbound tracks running at
ground level underneath the flyover – you will see essentially the same thing. There are four Down
platforms, from where trains can run to any of the four lines to the left, while the Airport line can
only be reached from 22 & 23. So looking at all the track at once here, you can see that both an
Up train and a Down train can cross over all the way from one side to the other, simultaneously,
without any conflict. You will also notice that the layout of the Down and Up lines
are basically clones of each other, with the Down lines just off-set to the east, and of course at a
lower height. Just quickly, there is one exception to all this directional trackage - inside the
tunnel towards the airport there is a crossover, and there is actually some bi-directional trackage
allowing an Up Airport train to come across and terminate in platform 23 in case of disruptions.
Now you've probably noticed that the bit where the Airport line branches off looks a bit odd, and you
might be wondering what's going on with this bit here, which has no track at all. This is because
the Airport line only opened in the year 2000, and before that, the whole flyover had a much neater
and almost symmetrical layout. In this condition it was also a genuine anywhere-to-anywhere
junction, with no limitations on which track you could access on the far side. When the Airport
line was cut in, the main Illawarra lines were modified to join the Illawarra Local lines on the
Down side of the flyover, which obviously reduced capacity from that direction, however it didn't
(and still doesn't) really matter, because most suburban trains on the Illawarra main run into the
underground Eastern Suburbs Railway which opened in 1979, and now this part of
it is only used by a handful of trains coming from Everleigh Maintenance Centre and the odd special
or unusual working. So the other important thing to note, is that if you look at all the trackage
coming in from the left, we're looking at five double track lines each with left hand running,
meaning the Up and Down tracks alternate. These lines are known as the Suburban, Local,
Illawarra Local, Illawarra, and Airport lines. But if you look on the other side of the junctions,
the platforms are arranged as four islands, with each island taking a pair of tracks leading in the
same direction, so from top to bottom there are two Up lines, then two Downs, two Ups,
and two Downs. To understand why the tracks have to be shuffled into this order, you need to have a
look at what happens over at the other end of the suburban platforms. After passing through Central,
trains can go in one of three directions. The North Shore line runs through the underground
via Town Hall and Wynyard stations, then up over the Harbour Bridge and off up towards Hornsby.
Then there is the City Circle which can be entered from either direction. The clockwise
tunnel is called the 'City Outer,' and the counter-clockwise tunnel is the 'City Inner.'
Note that as 'Up' is always towards Central and we've just jumped to the other side of the
station, that means red is now Up and Blue is now Down on this side of my diagram. Also note
I'm not showing the stations or other exact details in the underground area. There are
also a bunch of crossovers between Central and the tunnel entrances, giving some flexibility
in which platforms can be used. The ones I've coloured black run between Up and Down lines,
so are just for reversing direction in unusual circumstances. So that shows you how the track
is laid out, but it doesn't tell you how trains actually USE that layout during normal operations.
So I'm going to show the normal routes taken by regular passenger services, using the colours from
the official Sydney Trains map. The T1 North Shore & Western Line shown here in yellow,
runs from the Suburban lines on the left, through the underground, over the Harbour Bridge, and off
up the North Shore on the right. The T9 Northern line does exactly the same thing using the same
trackage, so I'm not going to bother showing it here. The orange T3 Bankstown Line comes in on
the Illawarra Local, and runs alternately around the City Inner, or the City Outer.
The light blue T2 Inner West line comes from the Local lines, heading around the western side of
the City Circle before mysteriously vanishing.. something that will make sense in one moment.
The green T8 Airport line comes in from the Airport and runs around the eastern side of
the Circle before also vanishing from the map. So what actually happens here, is that trains enter
the Circle on one side, then generally form a service on a different line out the other side. So
a train from the Inner West will become either a Bankstown or an Airport train as it passes through
the Circle, an Airport train will form a Bankstown or an Inner West service, and Bankstown trains
will be Bankstown trains.. or Inner West trains, or Airport trains.. This might sound like it would
be confusing for passengers, but in reality the information displays change immediately after
leaving Central, so it will be clear to anyone in the City Circle where the train is going.
During peak times, certain green T8 trains also bypass the Airport line, running on the Illawarra
Local directly down towards the East Hills line. So as you can see, the flyover is extremely well
utilised, and while some of the crossovers may not be required for everyday operations,
they certainly add a huge amount of flexibility in the case of disruptions or unusual movements.
So there you have it, a very clever piece of infrastructure that does a great job keeping
the people of Sydney moving. Hopefully that all made sense, and if I've made any mistakes it's
because I'm just some guy from Melbourne and not an official resource. Thanks for watching!