When the common traveler looks at Penn Station, they see 21 tracks, a handful of platforms, and trains from three different railroads. Even the most simple minded traveler can discern patters that emerge within Penn Station and the usage of its tracks, but very few know the reasoning behind it.
It would not be difficult to figure out that the majority of LIRR trains depart from tracks 13 through 21. In all the LIRR concourses and corridors there are staircases down to tracks 13 through 21 and there is practically no mention of the lower tracks. Furthermore, NJTransit commuters could pick up that, for the most part, their trains leave from tracks 1 through 12.
This segregation is one of the easiest things to pick up about Penn Station. The railroads are not integrated and the three different railroads, LIRR, NJT, and Amtrak, all have three different concourses. From there they have staircases down to the platforms they generally use and signs pointing to the other concourses, exits, and other various amenities.
And the concourses have been separated like this for quite some time. Each railroad maintains their little parts and finances upgrades to the spaces their passengers most frequently use. Each has their own signage and departure boards. While it is difficult to trace the origins of the divided concourses, when you look at the track layout, it is easy to see why the LIRR concourses serve certain tracks while Amtrak and NJTransit use the others.
The root of this comes from the layout of the interlockings around the station tracks: A, KN, C, and JO. There are five different "entrances" trains can come through as they approach Penn Station. From the east, they can arrive through East River Tunnels lines 1 and 2 (which are paired) or East River Tunnel lines 3 and 4 (which are also paired). From the west, trains can come into the station complex through either the two North River Tunnels, the one Empire Tunnel track, or the four West Side Yard Lead tracks.
In a logical station layout, a train would be able to get from any one of these five places (ERT 1&2, ERT 3&4, NRT, EMP, and WSY) and platform on any one of the 21 station tracks. However this is not the case. From any particular tunnel/yard lead entrance, you can only get to a certain range of station tracks. This therefore restricts what platforms trains coming from or going to certain places with certain equipment.
The following diagram I created illustrates just what tracks trains from the different "entrances" to Penn Station can end up on:
From this diagram, you can start to tell why certain trains leave from certain tracks. If you know that the LIRR makes heavy use of East River Tunnel lines 3 & 4, so this diagram gives evidence to why the LIRR typically uses tracks 13 and higher...ERT lines 3 & 4 lead to tracks 14 through 21, and a train from ERT lines 3 & 4 cannot end up on tack 8 or 11. There are occasions where a LIRR train can make their way into Penn Station through either lines 1 or 2, so therefore there can be occasions where a LIRR train might stumble onto track 11. But there are certain tracks in Penn Station at which you will never see a LIRR train. From the diagram, you can see that neither of the East River Tunnel pairs have access to tracks 1 through 4. Therefore, there will never be a LIRR train leaving from tracks 1 through 4, since that train would have no way of actually getting to Long Island.
Furthermore, other railroads have to work around these odd infrastructure obstacles. Amtrak trains that are operating through Penn Station from Washington to Boston or Boston to Washington, or NJTansit trains that want to continue to Sunnyside yard, musts arrive or depart from tracks five or higher, since tracks 1 through 4 can only be accessed from the west.
And there are also similar complications on the west end of the equation. Trains coming down the Empire Connection from Albany, Toronto, Montreal, Niagra Falls, Rutland, or Chicago will all enter the station trough this tunnel. However, once they get into the station, they can only platform on certain tracks, tracks 1 through 9.
Trains from the North River Tunnels have the most expansive reach, as those trains can access tracks 1 through 19, which only excludes two, tracks 20 and 21. Using this tidbit of knowledge, you can then see why you'll never see a NJTransit train leave from tracks 20 or 21.
And there are even more obstacles that restrict which trains can go where. The next major infrastructure obstacle is how the various station tracks in Penn Station are powered.
Within Penn Station, there are two different power systems (a trait unique to any rail complex in the country). There is overrunning 750V DC third rail that lies along certain tracks, while other tracks have 12kv, 25 Hz, overhead wire powering the tracks. And others have both.
The following diagram depicts which tracks are powered by third rail, which tracks are powered by overhead wire, and which tracks are powered by both:
Considering the fact that LIRR trains are powered by the third rail, you can use this diagram to tell that LIRR trains can only use tracks 5 through 21. A LIRR train on track 3 would not be moving much at all, since there is no third rail on those tracks.
NJTransit trains, on the other hand, are powered exclusively by overhead wire. At one point, all station tracks at Penn Station had12kV 25Hz overhead wire. However, about 8 months or so ago, the overhead wire was "temporarily" removed from tracks 18-21 and there is no sign of return, so, at least for the time being, NJTransit and Amtrak trains are incapable of platforming on anything higher than 17 track.
When you put these two diagrams together you get the following:
Then from this diagram you can see how the tracks certain trains can use are even further restricted. Let's take Empire trains as an example. 99% of Empire trains are powered by P32AC-DM locomotives, which get electric traction power from the third rail. So once you couple the tracks that trains from the Empire Tunnel can reach and the fact that the track the train ends up on has to be powered by third rail, you end up with a much more restrictive set of four tracks that Empire Service trains can use--tracks 5 through 9. Anything higher than 9 cannot be used by Empire trains since there is no way to get from the Empire Tunnels up to those tracks, and anything lower than 5 cannot be used by Empire Trains since those tracks do not have the third rail needed for the P32's.
All of these various infrastructure constraints contribute to a confusing set of conditions that arriving trains must comply to so they don't end up stuck someplace they don't want to be.
Compiling all of these different limitations together leads to the following diagram, which shows which services normally leave from what tracks. There are exceptions to these rules, as you can see Amtrak trains on higher tracks and LIRR trains arriving on track 5, but for the most part, the services adhere to something like this:
So now that we have a basic understanding of which types of trains depart from which tracks (and why), constructing the concourses on top of New York Penn's eleven platforms is the easier part. Logically, a certain railroad's concourse will be effectively positioned in the station at a location where passengers can easily access the tracks those trains usually depart from. It doesn't make much sense to have the LIRR concourse all the way at the south end of the station by tracks 1 and 2 where there will never be a LIRR train leaving from those tracks.
Ultimately, everything above leads to the concourse layouts depicted in the diagram below. The diagram below is merely illustrative, showing where each concourse is positioned and which tracks they serve. You can see the positioning of the NJTransit concourse allows easy access to NJT trains (tracks 1-12), the LIRR concourse lets you get at the LIRR tracks easily (tracks 13-21) and the Amtrak concourse lets you have a straight shot at the staircases where those trains depart from (tracks 5-16):
In this diagram, the upper level concourses are shown in blue and the lower level concourses are shown in gold. Here you can easily see how the lower LIRR concourses (the LIRR concourse, the Central Concourse, and the West End Concourse) are positioned to allow easy access to tracks 13 through 21. The the NJTransit concourse is positioned over tracks 1 through 12. The Amtrak concourse, which sits on top of all of them, has easy reach to tracks 5 through 16.
Revision 1/14/14: At a reader's request, I created one additional diagram of Penn Station to show the general locations of the former towers that controlled the Penn Station interlockings. In previous years, Penn Station's four interlockings, C, JO, A, and KN were controlled from four separate towers that had the same names, C, JO, A, and KN. When Penn Station Central Control was opened in 1995, control over these interlockings was transferred to PSCC and the towers were all closed. The following diagram depicts the general locations of the four former towers and the general location of the present-day PSCC:
At this point, the above diagrams hopefully give you a basic understanding of how and why some of the strange operating circumstances at New York Penn Station arise. There are countless other intricate other restrictions that are not covered directly in this post, (i.e. how LIRR Dual Modes are restricted from track 18 in Penn Station, etc.).
Please note: the above diagrams were created by The LIRR Today. Reuse without prior permission is not allowed. Please contact me for approval prior to reusing the diagrams.
Also check out this set of posts which takes a closer look at the platform tracks at Penn Station:
Tracks 1-4, Tracks 5-8, Tracks 9-14, Tracks 15-16, Tracks 17-19, Tracks 20-21