Here is one big diagram of the whole situation. Don't worry, there are more zoomed in diagrams below.
|(The diagram's so zoomed out that you can even see a bit of the Garden-Mitchell Secondary in the corner)|
Now I'm a bit fuzzy on the exact designations of NASSAU interlocking. I had always thought that it was one big huge interlocking that was not broken up into multiple parts (and that is how it is depicted in the diagram above). However, while doing some research for this post, I found out that some people consider NASSAU interlocking as broken up into four different parts (NASSAU 1 through NASSAU 4) like some other interlockings. But then again there are people that consider it one big piece like I do. I don't know exactly how the terminology plays out, but it's not all that important anyways.
Nevertheless, NASSSAU interlocking begins just east of New Hyde Park station. There is a pair of crossovers near Milepost 17. From west to east the crossovers go form Mainline 2 to Mainline 1 and then back to Mainline 2. The Chesler Plywood Siding hooks into the Mainline a bit to the west of where the diagram cuts off. That switch is not part of the interlocking.
After that the tracks continue through Merillon Avenue. After the Merillon Avenue the MoW track splits off from Mainline 2. This is a powered siding that spans almost the whole distance between Merillon Avenue and Mineola. Since there is no switch connecting it back into the mainline on the other end, the siding doesn't serve any significant service. It is pretty frequently used by MoW trains (hence the name), but there is little practical use for it.
The North Track is a short, non-powered, rarely-used siding that splits off of Mainline 1. It's good for storing four or five freight cars at most.
After that, the line continues through Mineola station. The switches just to the east of the station are the most notable, as here is where the Oyster Bay Branch splits off from the Mainline. There are two switches that take trains from the two Mainline tracks to the two Oyster Bay Branch tracks. The switch for track 2 is not a diamond switch (i.e. it is not possible fro a train to go from Mainline 2 to Mainline 1 or from Oyster Bay 2 to Mainline 1 or anything like that).
The switches are at-grade, which means an eastbound Oyster-Bay branch train will have to crossover the westbound Mainline and block traffic through there as well. This is part of the reason why the LIRR has considered truncating off the Oyster Bay Branch at Mineola, but there is currently a very small chance of that actually happening.
There are two grade crossings just to the east of the station (the Roslyn Road crossing has been replaced with a bridge and subsequently eliminated since this diagram was made). The Main Street crossing is particularly interesting because the switch points actually lie in the crossing. It's a busy crossing for a busy set of points, but they hold up pretty well!
After the station the North Side Track (which is different than the plain North Track) splits off from Mainline 1 and runs parallel to the Mianline for roughly three quarters of a mile. There are currently no active freight customers at this siding, so it sits dormant most of the time.
After that the line runs east a little bit more before finally going through one last pair of crossovers near Milepost 20. After that NASSAU finally ends...for the Mainline.
Not to be outdone, the Oyster Bay branch also has its own set of crossovers that are a part of NASSAU interlocking. These crossovers from Oyster Bay 1 to Oyster Bay 2 and then back to Oyster Bay 1 were installed here back in the days when the electrification ended at Mineola (they would turn electric trains along this branch to get them out of the way on the busier mainline). The crossovers used to be more to the north of this location, but their current position lends them perfectly to turning trains. (just like the one electric superlocal that originates at East Williston in the AM rush).
If you're from the "NASSAU 1" "NASSAU 2" "NASSAU 3" and "NASSAU 4" camp, I kept the diagrams in this post in order. The top picture and discription would be considered "NASSAU 1" and so on down to the East Williston crossovers being "NASSAU 4."
Signals, Towers, and all that Fun Stuff
NASSAU tower, a white-painted brick building, has seen its better days. While still an active tower, it's days are possibly numbered. Eventually, everything will be controlled by a few clicks of the mouse in the AirTriain building at Jamaica, and this tower does stand right in the middle of the path that the supposed third Mainline track would run on through this area.
But for now, NASSAU tower is alive and well, controlling the expansive NASSAU interlocking plus the comparatively puny LOCUST interlocking on the Oyster Bay Branch.
Not To Be Confused With...
Apparently NASSAU is a pretty common name for an interlocking in these parts. The Pennsylvania Railroad used to have an interlocking called NASSAU on the Northeast Corridor, just to the north (railroad east) of Princeton Junction station in New Jersey. The interlocking no longer exists, but the former tower on the site still stands and is used by Amtrak work crews on occasion.
That wraps up this winded Interlocking Walkthorugh. The nearest interlocking to the east of here is the equally sprawled out and nutty DIVIDE interlocking. To the west lies QUEENS interlocking (which, come to think of it, is also very crazy!)