KO interlocking, to the either side of Ronkonkoma station, is the easternmost interlocking on the Mainline. Located nearly 49 miles from Long Island City, it is the easternmost point in bot electrified territory and ATC signalling (see: MBS vs. ATC). This interlocking which sandwhiches a station also includes one of the LIRR's few carwash facilities, as well as a whole electric yard for trains.
Like several other interlockings, KO is split up into "KO 1" and "KO 2," with KO 1 falling to the west of the station platforms and KO 2 being the yard and switches to the east of the station. Below are two diagrams, one of KO 1 and one of KO 2, and here's a bird's eye view of the location.
Now let's delve right into the nity-grity. First, when coming from the west, the interlocking begins just before the Pond Road grade crossing. Just after the Pond Road crossing the Certified North Siding diverges off from Mainline 1.
To my knowledge, the Certified North Siding isn't used for all that much in day-to-day operations. It would be a pretty good place to store the Greenport scoot in between runs (kinda like they do at Huntington), but they'd rather sclep the scoot into and out of the yard in between runs, so this track sits largely dormant. Form time to time a LIRR MoW or NYA&R freight train might park itself here to get out of the way, but its use in normal passenger operations is limited.
After the Certified North Siding splits the Mainline widens to two tracks for its final stretch into Ronkonkoma. Mainline 2 diverges to the south of Mainline 1.
The Certified North Siding rejoins Mainline 1 closer to the station and there is one last crossover from Mainline 1 to Mainline 2, just in case a train wanted to go from the Certified North Siding to Mainline 2.
At that point KO 1 ends. The two tracks widen to fit in between Ronkonkoma's three platforms (another trait unique to Ronkonkoma station).
Almost immediately to the east of the station platforms KO 2 interlocking begins. There is a 20 m.p.h. speed restriction in place through the entirety of KO 2 interlocking. Mainline 1 and 2 scoot a little closer together and a third track splits off from Mainline 2. This track, called the WASH track by its cool friends, houses one of the LIRR's three remaining car washes (the other two being at Babylon and Richmond Hill). Trains looking to go for a spin through the car was must come through Ronkonkoma station on track 2 to be aligned to go through it.
Following the car wash there is a double set of double crossovers. The four switches go as follows: from Mainline 1 to Mainline 2, from Mainline 2 to Mainline 1, from the WASH track to Mainline 2 and from Mainline 2 to the WASH track. These switches allow a train from Mainline 1 to get to either Mainline 2 or the yard, a train from Mainline 2 can get to either Mainline 1 or the yard, and a train from the WASH track can get to either the yard or Mainline 2.
The next track structures we reach is the Ronkonkoma Yard. The Ronkonkoma Yard consists of twelve tracks numbered 0 through 11. The tracks are split up into two clusters, 0-4 and 5-11.
Tracks 5-11 branch off of what was the WASH track. After exiting the Car Wash a train would have direct access to yard tracks 5-11 (with access to the other yard tracks being accessed via one of the above mentioned crossovers). The other group of tracks, yard tracks 0-4, all branch directly off of the mainline, not the WASH track. All but one of the tracks (track 0) are stub-ended, meaning that the train going to the yard simply meets a bumper block at the end of the track and nothing else. Track 0 is the lone exception to that rule. Track 0 is the only track that merges back into the Mainline. Track 0 is frequently home to the Greenport Scoot. Parking the scoot on track 0 overnight is usually a good move, because in the morning, the first maneuver the scoot has to make is a deadhead run from KO yard to Greenport, and if the train is on track 0, it can just take off east from the yard. If it were on any of the other tracks it would have to reverse back towards the station before proceeding east.
All tracks at Ronkonkoma Yard are powered, and the yard is frequently very full overnight storing all sorts of trains from the evening rush (because, remember, the Ronkonkoma Branch is single tracked for most of its length, so once the rush hour has gotten underway, there's no way to deadhead trains in the opposite direction, everything has to go into or out of the yard).
Shortly after track 0 merges back into Mainline 2 the Ronkonkoma Team Track splits off Mainline 2. The Team Track, which used to be one leg of a now long-gone wye at Ronkonkoma, currently does not have any customers that receive cars there.
Shortly after the team track splits off the Mainline is finally reduced from two tracks to one for one last time.
The third rail ends just before the Knickerbocker Avenue crossing, right after the two Mainline tracks converge back into one.
The eastern limit of KO 2 interlocking is located a couple hundred feet to the east, closer to the Coates Avenue crossing. The eastern limit of KO 2 interlocking is also the eastern limit of ATC territory on the Mainline. From this point east it's all Manual Block (see MBS vs. ATC for more on this difference).
Shortly after KO 2 interlocking ends the 20 m.p.h. speed restriction is lifted and the speed limit is again raised to 45 m.p.h., which is the speed limit for all trains between Ronkonkoma and Riverhead.
KO interlocking is still home to a variety of older position light signals. In the coming decades KO interlocking will likely be done over once again and new signals will be installed, but for now pretty much everything is original back to the time when electrification was extended to here in the late 1980's.
There was never a KO switch tower at this location, everything has been controlled from DIVIDE tower since the interlocking was put into service on December 14, 1987.
That wraps up today's interlocking walkthrough. KO's one and only neighboring interlocking is CI interlocking one station to the west. Next week's interlocking walkthrough will visit one of the LIRR's few remaining active drawbridges, LEAD drawbridge over the Reynold's Channel.