Interlocking Walkthrough: CI

Next up in our series of Interlocking Walkthrough's is CI interlocking, in Central Islip.  This interlocking sits along the Mainline (a.k.a. Ronkonkoma Branch) and it is a frequent place for trains to meet each other during rush hours.  Here's a bird's eye view of the location.  This interlocking is fairly simple; here's a diagram of the interlocking:

As one can tell, CI interlocking, similar to BROOK, is split up into two smaller interlockings, CI 1 and CI 2.  CI 1 is the interlocked switch to the west of the station platform, and CI 2 is to the east.

Switches
CI is your stereotypical passing-siding-in-single-track-territory interlockings.  It's very similar to interlockings like DUKE, FOX, POST, and STONY on the Port Jefferson Branch in the regard that more often than not, we have a single track main, it splits into two tracks before entering the station, passes through the station with platforms for two trains to meet there at once, then converges back into one track for the remainder of the trip.

So a train coming east, after going from double-track to single-track territory at BRENT interlocking, travels along the mainline and then encounters CI 1.  At CI 1 the SIDING track splits off from the MAINLINE one, passes through the station, then crosses over Lowell Avenue, before entering CI 2 and converging back into one track once again.  The Mainline then continues east as a single track all the way to Ronkonkoma.

The main purpose of CI interlocking is so that trains going in opposite directions can meet at Central Islip, using the two tracks, then proceed off on their merry ways in either direction without getting in each other's way.

At Central Islip, the majority of trains use the MAIN track (indicated as platform A in the timetables).  Platform B along the SIDING track is really only used when trains meet at Central Islip, or when the schedule makers in Jamaica want to spice things up a little and send a train to Platform B for the fun of it.

Signals
CI interlocking has the "old" position light signals (the big round ones on with yellow lights).  There are four sets of signals, on either end of the two interlockings.  The two sets of signals closest to the station on either side (at the eastern limit of CI 1 and the western limit of CI 2) are on gantries, while the signals at the outer two limits are signals mounted on the side of the tracks.

Towers
There is no CI tower located here, and there never was.  CI interlocking was only put in around the same time when the LIRR electrified the mainline from Hicksville to Ronkonkoma.  Before that, it was only single-tracked through the area.  Anyways, the interlocking has been controlled from DIVIDE tower in Hicksville since day one.

Neighbors
CI is bordered to the west by BRENT interlocking in Bentwood, and KO interlocking to the east near Ronkonkoma.  It's a strikingly long way to KO interlocking, and if a train becomes delayed, it's between these two points where the delay minutes really start to pile up, because a late eastbound train has to clear the big stretch of single track territory between CI and KO before a westbound train can come west.

This is one of the main reasons why the Ronkonkoma Branch Double Track Project would have the first section of new double track installed between Ronkonkoma and Central Islip.

The speed limit through here is a brisk 80 m.p.h., though the trains diverging off to the SIDING track have to slow down a tad so they don't derail going off on the switch.

~~~~~~~~~~

Before I wrap this interlocking walkthorugh up, I'd like to mention I've set up an Interlocking Walkthorugh Index where you can quickly find the interlocking walkthrough you're looking for. You can quickly get to the index page by clicking on the "Interlocking Walkthorugh Index" link in the "Popular Links" box at the very top-right corner of every page on this site.