There's a lot of work taking place on the former PRR Northeast Corridor these days and unfortunately it appears that the era of main line pneumatic point machines might be nearing an end. The stock of pneumatic interlockings had been dwindling for years with LANDOVER near Washington, DC, GRUNDY in Bristol, PA and FAIR in Trenton being the two latest to see wholesale conversion to electric US&S M3 style machines. Prior to that both THORN and PAOLI interlockings on the Harrisburg Line saw their pneumatics go even while their interlocking towers remained open.
Currently, what had been some of the best preserved main line pneumatic interlocking plants, RIVER and POINT at the north end of Baltimore's Bayview yard, are in the midst of an electric conversion as their turnouts are being replaced as part of a general maintenance project.
Unfortunately, due to their location, these two locations are difficult to photograph except from the rear of passing Amfleet equipped trains.
This will leave what is in my estimation only a single intact pneumatic main line interlocking plant, HOLMES, at Homesburg Jct in Philadelphia. OVERBROOK interlocking, with its staffed tower, is still largely pneumatic, but had seen select turnouts replaced with M3's.
Of course a significant number of terminal plants will remain pneumatic for the foreseeable future and one could possibly count terminal adjacent interlockings like Metra's TOWER A-2 and SEPTA's 16TH ST as Main Line as well, however neither see the high speed movements currently present at RIVER, POINT and HOLMES. The challenge for documentation is capturing the movement and sounds of the switches as they throw. At HOLMES this is most easily covered when local freights enter and exit the Buttleton branch, but this could also be achieved when tracks are out of service east or west of the plant. Of course the easiest way to engage with pneumatic point machines is to see them on rapid transit systems such as The PATH, NYC Subway and the SEPTA Broad Street Line.
