LOCUST interlocking, located at the outer edge of the Oyster Bay Branch is right next to Locust Valley station. LOCUST interlocking is where the Oyster Bay Branch goes from two tracks to one. West of here, the Oyster Bay Branch is double tracked all the way to NASSAU interlocking where it joins the mainline, but the line is single tracked east of this location to the line's end at Oyster Bay, one station to the east. Here's a birds eye view of the location.
LOCUST interlocking is simple in nature, shorty after Locust Valley
station the line goes from two tracks to one and that's it. One simple
To this day the tower at LOCUST interlocking still stands, and in recent years it has been restored to its original condition. The tower now serves as a police booth for the NCPD Second Prescient.
The three signals remaining at this simple interlocking are "old style" position light signals. In the coming years the signals at LOCUST will be replaced in the LIRR's bid to modernize the system and bring control of everything under one roof at Jamaica. But for now, NASSAU tower at the western end of the Oyster Bay Branch does the honors of switching this interlocking's lone switch.
The speed limit for trains traveling on the Oyster Bay Branch drop down at the eastern limit of this interlocking, from this point forward, trains can go no faster than 40 m.p.h. on the remaining and very curvy portion of this branch.