Inside the US&S A-5 Switch-Point Machine

This blog devotes a lot of coverage to the plight of the pneumatic switch-point machine and its long decline since its heyday between 1930 and 1955, but apart from the ka-chug--woosh sound, what makes them distinctive? Well its actually their simplicity compared to their electric counterparts and its that simplicity that made them so competitive with electric point machines despite the overhead of making and distributing compressed air. 

Above we see a Union Switch and Signal model A-5 pneumatic point machine. (An earlier A-1 model also existed and you can tell them in photos because the housing looks like a miniature Quonset hut.) At one end we see the double acting air piston, at the other we see a connection for the control circuits and a blind tube without an air piston, and in the middle we have a fairly plain looking box.

Next lets quickly go over a standard power operated switch layout using some casual terminology. Moving away from the camera we have a stretcher bar that provides rigidity. Next is the throw mechanism that transmits force from the point machine to the points via a rod. This uses a slack coupling so the point mechanism can begin to move and break the static friction. Finally we have the detection rods that accurately detect if the points are hard against the stock rail and communicate that state to the signaling system.

Exposed US&S A-5 pneumatic point machine.

The mechanism can be set up for operation from either side.

Here we see a naked A-5 without its cover on showing off the simplicity of the action. The air piston connects to an action bar which runs through a crank mechanism that transmits force to the point rodding and also its positional state to the circuit controller.

The crank (left) and circuit controller (right).

The coupling between the air piston and the action bar.

The air piston, these came in 3 inch and 5 inch diameter models.

The throw rod couples to the crank assembly. In the photo below this connection is the bolt hole on the stubby arm below the pivot pin. The detection rods sit under the circuit controller have the golden coated nuts on them.

The circuit controller pulls double duty, detecting both the position of the points for the signaling system and also the position of the action bar / air piston, which is sent to the style CP air value unit to cut the flow of air and dump the pressure in the piston. We can see the hind end of the action bar that is given room to push outward under the covering.

The upper two rods provide the actual point detection while I believe the lower rod that extends through the mechanism provides a physical locking function in conjunction with the action bar. When this technology was new that rod would serve the role of the familiar facing point lock.

The goal of the mechanism is to lock the switch point securely against the stock rail even when air pressure in the cylinder has been exhausted, but allow smooth movement of the action bar and points when air is admitted to move the piston. A similar concept is present in firearms where the bolt is locked against moving rearward by the force of gases in the chamber, but is able to be easily unlocked via motion in a different axis.

While I have personally captured video of an A-5 point machine performing a throw cycle, it only showed the points moving along with the admittedly cool sound. However I recently came across a different video from a UK rail museum that has their own flavor of a US&S A-series set up for live demonstrations. Still popular on the London Underground, these instances are commonly used without the protective cover which allows visitors to actually see how the mechanism functions. This flavor of Westinghouse point machine is intended to be set between the rails and has the throw rods moving through the mechanism. The extra circuit controller on the back provides feedback to the pneumatic value.

 

No Approach! The Duality of Uncommon Signals

We all learn about traffic lights in elementary school.  Red means stop, green means go and yellow means slow or caution. These are the basics of automatic block signaling that also tend to get taught in entry level railroading books. Now its pretty logical that a signal might lack the ability to display a clear indication. A permanent stop condition or the end of automatic block territory are both situations where a Clear signal would not ever apply. However there are a few situations where signals in North America can display Stop or Clear, but not Approach on the full speed head. 

The first is at interlockings outside of automatic block territory like a diamond crossing or drawbridge. The signal provides movement authority through the interlocking and without track circuits outside of the interlocking limits there is no "prepare to stop" points an Approach type signal would apply to. Trains will have their own movement authority like a track warrant so a clear signal is basically the interlocking telling the train "you do you". One might expect signals in this case to display a Restricting indication, instead of a clear, and sometimes they do, but that is going to come with a 20mph speed restriction, or less, which can be a time hit on unsignaled lines with higher track speeds. 

The next situation, Manual Block territory, would be very familiar to those in other parts of the world. Although almost extinct in the US, there remains a bit of manual block still in service on the LIRR and the way to identify a manual block signal is the lack of an approach indication. (This also applies in general to historic PRR signaling charts.) Signals will display Stop or Clear Block with any Approach functionality handled by a separate distant signal towards the end of the manual block. The PRR even went one further sometimes substituting the \ "Caution" indication in place of / Approach. 

Sometimes its really not good to have locomotives stopped and waiting at a specific signal,  Maybe there's an issue with a grade crossing, or noise, or diesel exhaust. In this case it would not be desirable for trains to approach that signal prepared to stop, so a preceding signal will either hold trains short or allow them to approach a signal with some sort of proceed indication. The most notable of these is at the entrance to Washington Union Stations 1st St tunnel that the currently diesel hauled northbound trains cannot enter without having a signal displayed further on that allows them to leave said tunnel. Another nearby signal location at CSX's LENFANT interlocking might lack southbound approach signals for a similar reason due to an overbuild.

One somewhat PRR-specific situation is where interlockings are provided with exit signals and because of the short distance between the interlocking's entrance signal and exit signal, Slow Approach is used instead of Approach. This creates an upper head that can only display --- Stop or | Clear. The C&O also made frequent use of exit signals, but seemed to keep their upper head Approach indication, although Medium Clear to exit Approach allowed the C&O to minimize the use of R/Y/Y/ Medium Clear.

A fairly new situation where Approach has been "omitted" involves high speed turnouts. At certain points on the NEC, Amtrak has decided to combine a flashing green "Cab Speed" signal indication with R/*Y* Medium Approach. At the end of a main track that converges into another via a high speed turnout, the result will be an upper head with green and red lamps/positions and no yellow lamp/position.
 

New Signals Up At THORN

 Although not much has changed regarding the ultimate fate of THORN tower, recent photos do show what the new signaling situation is going to look like. In the eastbound direction the triple signal bridge covering tracks 1, 2 and 5 Running, have gotten the Safetrain upgrade with Rule 562 'C' boards turned. Although not yet in photos, it is expected that track 4 will also be getting a PL mast signal to replace the existing reverse direction dwarf. SEPTA is tentatively resuming service to Coatesville upon the completion of new station facilities in 2025 which includes a semi-restoration of #2 track to a point just past the new station for the daily NS regional freight. 

In the westbound direction new PL masts are up on tracks 1 and 2 to replace the reverse direction dwarfs and its assumed that a new gantry mounted signal will be in store for #4 track.  The real surprise is what looked to be a new westbound full PL mast signal on what used to be the Low Grade Freight Line track. The old THORN had maintained a vestigial signal in that same location, but despite the rationalization of the former 6-track full crossover, it seems the low grade stub track has not only been retained, but is being prepared for use. What that use might be remains to be seen, but a mast capable of displaying Medium and Limited speed signals could imply SEPTA trains making some sort of switchback maneuver after discharging on Thorndale's track #4 platform or coming out of some yet to be built storage tracks on the footprint of the old PRR Thorndale facility. 

The THORN interlocking cutover is still planned for later in June with DOWNS to lose its switches before complete removal. GLEN and FRAZER will be turned over to the dispatcher by the end of 2025 closing THORN as an active interlocking station.

Harrisburg Power Office Is Now Mostly Up and Running

When we last checked in on the Harrisburg Power Director's office about a year ago in 2024, the Big Board had been fully illuminated and most of the Westinghouse "Visicode" SCADA equipment had been reactivated with the help of modern technology simulating the presence of the field equipment like substations and such. However, because the 1930's PRR electrification projects had been funded with depression era WPA loans, the PRR had to spread the wealth and about half the office used GE "Code Selector" hardware that was more complex in operation and not as well documented. 

Well between March and September 2024, members of the Harrisburg Chapter NRHS managed to locate the documentation for the GE gear (it was sitting on a storage shelf) and were then able to restore most of the GE panels to operation, which is especially useful that represents the bulk of what was still operational on the old PRR Main Line up through 2013. The GE gear brings the added fun of step switches being used to store digits instead of all-relay registers for the Westinghouse part of the office.

As if step-switches weren't enough, between September 2024 and March 2025, the team also reconnected the alarm lamps and bell which further adds to the effect.

Still to be addressed are the metering circuits along with programmed simulation elements that would allow visitors to participate in directing flows of 25hz power to virtual train movements. Still, the Harrisburg power office  is mostly complete in terms of being "a thing that functions as it once did" so watch out for planned opening dates as the chapter is still trying to figure out how to manage regular hours.

DOCK Movable Bridge to Become DOCK Bridge

In 2017 the great DOCK tower closed as a staffed interlocking station after about 80 years of service. However the imposing structure retained one last official duty beyond "employee lounge" and that was housing the controls and auxiliary equipment to work the adjacent three span vertical lift drawbridge situated between the tower and Newark Penn Station.

 

Unfortunately the Passiac River was not the industrial thoroughfare of years past and unlike the nearby PORTAL bridge whose low clearance made it subject to periodic openings for barge traffic, the height of the DOCK draws is sufficient for the dwindling commercial traffic on the waterway.  After not opening a single time in 2024, Amtrak has petitioned the Coast Guard for permission to permanently close the bridge.

While it is unlikely that anything will happen to the bridge, Amtrak will no longer have to maintain the operating equipment, interlocking logic and the mechanisms used to make and break rail and overhead wire continuity.

DOCK draw actually contains three independent movable bridge spans. A large 3-track north span for mostly westbound Amtrak and NJT trains, a 2 track span for PATH rapid transit trains and a single track span for mostly eastbound Amtrak and NJT trains. The PATH span was set at a higher clearance above the river to reduce the number of openings on what was higher frequency rapid transit line.

 

One interesting quirk was the use of standard point machines to work the rail locking mechanisms at least on the PATH tracks. 

Based on the general interlocking layout I would not expect many signals to move, although the eastbound signals on tracks 2 and 3 might be moved across the bridge to resolve possible ACSES positive stop issues.

The fate of the control equipment on the operator's level and the auxiliary equipment, like AC-DC motor-generators, on the cavernous ground floor remains to be seen, however the safe option would be to leave it in place just in case. Numerous lift bridge have been converted to a fixed status with the counterweights left to dangle for many decades with little thought.

The petition requires a 120 day trial period of being "closed" at which point it will be approved or denied. After that there would be no set timeline for Amtrak to make changes so if a signal move looks likely I'll keep you informed.

Cleveland Line Autos Now on the Way Out

 In another example of either speaking too soon or rolling under the lowering door like Geordi, it has been reported that NS is planning on removing the remaining Cleveland Line ABS Position Lights I recently reported on. 

Scuttlebutt is that NS actually needs the parts to maintain the PL's on the western Fort Wayne Line, however I suspect that after the East Palestine explosion closed the Fort Wayne Line, the lack of PTC on the lower Cleveland may have become an issue. No word on the timeline, but I'll try to track the progress and if the project is a 1 for 1 signal replacement or something that will convert the line from ABS to CTC.

THORN Tower's Last Act

Amtrak's THORN tower has been staffed 24/7 and routing trains on the former Pennsylvania Railroad Main Line since 1938, however after having gone on a rather extensive diet in recent years, THORN tower appears to be entering its last act. However its not going without a few strange twists.

As a CTC era tower with both local and remote relay based interlockings, THORN presents a fairly easy case for remote control, as was the case with THORN's sister tower COLA back in 1987. Already Amtrak has chipped away at THORN's territory, re-signaling CALN interlocking and transfering control to the Section C dispatcher in 2020.  Now it appears that the plan is to re-signal and transfer control of the local THORN interlocking in the middle of 2025.  

While this would typically mean the closing of THORN tower itself, the news is that the tower will continue in service controlling GLEN interlocking via the 1938 CTC machine and FRAZER interlocking on the 1994 vintage unit lever panel. Much of THORN's work involves FRAZER interlocking as that is where SEPTA trains for the busy R5 Paoli/Thorndale service lay over.

Plans also include the removal of DOWNS interlocking with deadhead movements continuing on to THORN. For years track #2 between THORN and GLEN had been in terrible shape with Amtrak operators and dispatchers looking for ways to avoid using it.  However it has been recently rehabilitated and train managers are looking to make better use of the asset. 

With these changes I would expect to see "C" boards for Rule 562 operation on both sides of THORN and if DOWNS is removed it is possible that cab signal only operation will extend all the way to FRAZER (track #1) and GLEN (track #4). Whatever happens, I'll keep everyone informed.

PHOTOS: Amtrak CORK Tower

 A while ago I posted the first part of my coverage of the Pennsylvania Railroad's 1929 CORK interlocking tower in Lancaster, PA which covered the tower's history and the layout of the interlocking on the PRR's Main Line. Today we cover the tower itself, heading inside to see how it functioned in both its pre and post re-signaling phases. The exterior photos date from 2005 when the interlocking complex was in the process of being resignaled. 

To recap, CORK interlocking and tower were constructed as part of the 1929 Lancaster station project which moved Lancaster's busy passenger depot away from a downtown alignment with slow speeds, lots of grade crossings and partial street running. The resulting interlocking plant spanned approximately 3.3 miles of main line track, which was an outlier for early 20th century direct wire controlled interlockings in North America. Like the contemporary Lancaster station. CORK was built of a dark brick and featured a prominent bay window sheathed in copper cladding. 

 

 

The tower had one auxiliary building that housed the primary compressed air plant and was situated on the south side of the tracks in line with the extreme west ends of the high level station platforms. The tower had an internal staircase with the shelf type relay room on the first floor. With its brick construction and slate roof, the tower was in excellent physical shape as it entered the 21st century. 

 

Heading inside the tower we find a typical layout with the operator's desk sitting in front of the US&S Model 14 interlocking machine. A defect detector readout and overhead catenary section breaker control panel are to the operator's right with the lockers, clock and old telecom plugboard sitting to the left. One interesting feature is that the room has retained its original 1929 vintage overhead lamp fixtures. 

The operator's space is feels like a more cramped version of HARRIS tower with less space around the interlocking machine on all four sides. The gap between the scoreboard style model board and the rear aligned internal staircase is particularly small. As with other PRR Main Line towers, lever blocking devices are stored on top of the interlocking machine and the bathroom is in the left rear corner. Also note the location of the refrigerator, notice board and train order hoops. 

The sprawling CORK interlocking plant was controlled by a relatively modest 67 lever interlocking machine with 49 active levers in its 1960's configuration consisting of 23 levers for switches, 23 levers for signals, 2 levers for electric switch locks and 1 crossing lever for the Reading's Lancaster Branch diamond crossing. The plant was divided into three timer zones, A, B and C with the A timer handling the Conestoga section, the B timer the central Cork plant and the C timer the Reading crossing. The short run was 1 minute with the long run being about 5 minutes and 30 seconds. The tower also had 4 horns for Conestoga, the tower itself, Lancaster West, Dillersville yard and the Reading crossing (Longs Park).

One interesting feature was the presence of Rusty Rail tabs instead of the more usual placard. Besides that the levers were of the standard US&S crank type.

Although CORK's model board was a standard PRR illuminated type, it had several interesting features features. Grade crossing status lights were located at either end of the board to indicate the activation status of the Irishtown Road (east) or Eby Chiques (west) crossings. There were three low air alarms for East and West Conestoga in addition to the Cork main plant. In the post-1960 era two block indication lamps were added for tracks 1 and 4 eastbound. These had some interaction with PARK tower to the east as well as the intervening temporary block station at LEAMAN with track #1 being lit by the regular 2 lever and track #4 by a button on the operator's desk console. Best I can tell this was some technical method to prevent conflicting movements beyond what would be afforded by train orders and the dispatcher. Finally the most endearing model board feature was a framed photo of CORK tower itself that is also present in photos from c. 1992.

 

Hidden Gems - Cleveland Line PRR ABS Signals

The whirlwind of PTC motivated re-signaling has wiped out vintage ABS and CTC systems all across the country including most of the main line PRR position lights. However in one tiny corner of Pennsylvania not only exists a remnant population of PRR position lights, but position lights in a single direction ABS configuration. The Cleveland Line between CP-ROCHESTER (Conway Yard) and Alliance, Ohio serves as a backup route for the far more popular Fort Wayne Line. Due to the low traffic volumes is it PTC exempt, which explains how the PRR era signals have hung on. All together there are 6 PL signal locations on the dual track ABS segment between Rochester, PA and Yellow Creek, OH and today I will cover them all in an eastbound direction using photos that were taken over three trips in 2021, 2022 and 2023. 

The first location is at milepost 22 at the east end of Wellsville, OH. It consists of one eastbound PL mast and a new westbound Darth Vader mast that was installed in the late 2010s when CP-YELLOW CREEK was re-signaled. It is located just outside the flood wall and is lit full time with PL signal 221 displaying clear by default and signal 222 Approach.

The next location is at milepost 19 right behind the football stadium of Westgate Middle School in the town of East Liverpool, OH. It consists of two single head PL masts, both continuously lit with a Clear signal indication.

The location is also notable for the presence of 1940's vintage Carnegie steel rail and a somewhat ad hoc run of signal wire between the cabinet and rails.

In the East End section of East Liverpool at the site of the closed Virginia Ave railroad crossing we find the milepost 16 location with another pair of PL masts. This time signal 164 displays Approach by default due to a pair of interlockings, VEZ and MIDLAND, at either end of a single track section a few miles to the east to the east. Because the track #1 does not encounter a diverging route at VEZ interlocking the corresponding PL mast needed no modification and was therefore not replaced. The short single track section seems to have been installed due to the risk of RoW erosion by the Ohio River, but also acts as a "Conrail Crossover". The eastbound 164 signal is also significantly taller than the opposite 165 mast.

The relay cabinets associated with the signals display both US&S and Wabco logos.

Seeing as VEZ and MIDLAND took out the following two ABS locations, the next automatic signal location is across the PA border, just east of te town of Midland and directly adjacent to state route 68 at milepost 8.6. It consists of an eastbound position light and westbound Darth Vader which are lit full time with Clear the default indication eastbound and Approach the default westbound. They are co-located with the Midland hotbox, dragging equipment and high car detector.