In this diagram below, Bethpage and Hicksville stations are off to the top-left (northwest), Farmingdale station is off to the right, and the Central Branch towards Babylon station is the yellow line diverging off towards the bottom of the map.
In the near future I'll make a post all about the mysterious, stationless Central Branch and all it's uses, but for now we'll just focus on the little segment of it that appears here.
This interlocking is fairly simple in form and function. An eastbound train coming from points west approaches the interlocking and can switch from either track to the other. First there's a crossover from Mainline 2 (eastbound track) to Mainline 1 (westbound track), then there's a crossover back from Mainline 1 to Mainline 2. Then the Central Branch (the yellow line) diverges off to the right from Mainline 2.
The Mainline tracks (purple) then curve off to the left, cross over the Merrits Road crossing before proceeding east towards Farmingdale, Ronkonkoma, and Greenport.
Going east/south on the Central Branch the tracks rise up a little to pass over Hempstead Turnpike/Conklin Avenue (whatever it's called at that point) and then over Merrits Road. Just before the Conklin Avenue overpass the third rail ends (as the Central Branch is used only by diesel trains) before proceeding east a little bit more where the interlocking itself ends.
The switches here are set up in such a way that a train can come off the Central Branch and quickly switch to either of the two mainline tracks right there without having to go the wrong way on a track for a stretch.
BETH interlocking still retains the traditional position-light signals. The signals for the two mainline tracks at either side of the interlocking are on gantries, and the two signals on the Central Branch (just to the east of the Merrits Road overpass) are stand alone on the right sides of the tracks.
BETH interlocking used to be the site of B tower, which would control the switches and signals for BETH interlocking, among others. (Note how the name of the tower and the name of the interlocking are different, something not very common on the LIRR.) Since B tower was closed some time ago all of the switches and signals are controlled from DIVIDE tower near Hicksville a couple miles to the north.
Here's a photo from TrainsAreFun.com of B tower while it was still in service:
|(Photo credit: Jim Gillin/Trains Are Fun)|
You won't have to go all that far to find another interlocking on the Mainline, DIVIDE interlocking to the west is just a couple miles away near Hicksville and FARM interlocking to the east near Farmingdale station.
On the Central Branch you'll have to go all the way to BABYLON interlocking to the south. (Though there is the Wellwood Double End freight siding near Wellwood Avenue that could be used to pass trains in a pinch)
The speed limit through BETH interlocking itself is limited to 60 m.p.h. However, the speed limit upgrades to 80 m.p.h. on either side of the interlocking for the mainline tracks and 65 m.p.h. for the Central Branch.
Next week's interlocking walkthrough takes us a bit east of this location on the Mainline to BRENT interlocking.