the stub platforms don't have third rail on those tracks, so that renders them useless to the vast majority of Empire Service trains, since they operate almost completely with P32AC-DM engines, which need third rail power to operate in electric mode.
Empire Service trains are also able to use about half of 9 track at Penn Station, and you can occasionally see the shorter Albany trains on that track, but, for the most part, Empire trains stick to tracks 5 through 8.
Furthermore, since these tracks are connected to both the North River and East River Tunnels, they are frequently used by various Amtrak trains to places on and off the Northeast Corridor. Trains terminating here can also continue through to Sunnyside Yard in Queens where they can be serviced.
5 track also has another unique feature. At the east end of the platform there is a short pocket track that splits off and ends in a bumper block. The pocket track, which is long enough to store a locomotive, could be used to keep a protect engine or a yard switcher. Don't quote me on this, but the last time I took Northeast Regional train 179, which is one of the only Northeast Regional trains that comes from the east and terminates at Penn Station, I'm pretty sure I remember seeing an AEM-7 camp out on that pocket track and when the train arrived, the AEM-7 attached itself to the back of the train and took the equipment to Sunnyside Yard. Northeast Regional trians don't commonly have cab-cars, and I would imagine reversing a train through the East River Tunnels is frowned upon, so this seems like a logical workaround, but it's been quite some time since I last took that train.
Rumors have held that the pocket stub coming off of 5 track, along with the four stub tracks to the south of 5 track, would continue eastward into a possible fifth and sixth line under the East River. There are a number of physical obstacles that restrict such expansion today, and those would have to be worked around before any continuation of those tracks can come to be.
Lastly, to bring up every Westchester County politician's favorite rail project, Penn Station Access, it is worth pointing out that if Metro-North Hudson Line trains were ever sent down the Empire Connection and into Penn Station as it exists today, these would be the only four tracks Metro-North would be able to make use of. This is notable because, first, for Metro-North to obtain track slots on these four tracks they would have to deal exclusively with Amtrak and NJTransit. No LIRR trains use these tracks, so it's not like they can trade over some of their old slots when East Side Access opens. It might be possible to shuffle some trains around by moving NJTransit/Amtrak trains up to the higher tracks and thus allowing Metro-North to get some slots on tracks 5-8, but it would likely involve more trouble than it would otherwise.
Relief may be coming for those Empire Service riders who are looking for a little more variety in their track assignments, however. As part of Amtrak's Gateway Project several parts of A interlocking will be rearranged, particularly some of the crossovers on the X-leads (tracks 1X-6X which funnel into the North River Tunnels). If they succeed in their venture, trains from both the Empire Tunnel and the two new Gateway Tunnels would be able to reach tracks as high as 13 track. While it's not the whole station, it will offer far more flexibility into and out of Penn Station for trains coming in through the Empire and Gateway Tunnels. If you're familiar with the diagrams I first put out on Monday, I've revised the tunnel diagram to show how things would be laid out following the completion of the Gateway Project (whenever that may be):
In a few decades New York Penn Station will be a completely different animal. At the moment, it is a wile rhinoceros that is always bumping into things and stepping on things that shouldn't be stepped on. It works pretty well at the moment, but it is very cramped and a lot can go wrong with even the smallest hiccup. Eventually, Penn Station will have a design that will feature a lot more platform space, redesigned interlockings that will expand options and flexibility, and hopefully a new station house sitting on top of it all to boot, but many of those plans are still several years off.
Jump to other posts about New York Penn Station's Tracks:
Tracks 1-4, Tracks 5-8, Tracks 9-14, Tracks 15-16, Tracks 17-19, Tracks 20-21