Operator Duties

An Operator's Duties

Mark's Railroad-Related Stuff
A Pennsylvania Railroad Home Page
Railroad Books of Rules and Signalling: A Home Page
Operator's Duties

I wrote this up for the Signal discussion group in January 1996 from my own recollections of watching tower operators in many locations, but with the most time spent in the Harrisburg-Lancaster area of Pennsylvania. I hope this is informative and enjoyable. Corrections and comments are welcome, as always.

Let's say the territory looks like this (you may wish to print this out in a monospaced font):

The Map of the Territory

  -+-               -+-       -+-         -+-       -+-           -------|--->>
   |             OO--|6L   O=--|        O--|         |          9/   OO--|6L
 6R||-o  3 \ / 5 OO--|4L   O=--|        O--|       6R||-o  \3 7/  /11 o-||4L
 4R|--OO 1/   \7  o-||2L       |--O        |--=O   4R|--OO 1/ \5      o-||2L
 2R|--OO             |         |--O        |--=O   2R|--OO               |
  -+-               -+-       -+-         -+-       -+-                 -+-
       ITLK "ABEL"            2711        2689            ITLK "BAKER"
          273.4               2710        2688                266.4

                            -+-         -+-       -+-                   -+-
                         O=--|        O--|         |                 OO--|
                         O=--|        O--|         ||-o 1\       /11 OO--|
       continued             |           |         ||-o   3\   /9     o-||
                             |--O        |--=O     |--OO   5/ \7      o-||
                             |--O        |--=O     |--OO                 |
                            -+-         -+-       -+-                   -+-
                           2643        2621            ITLK "CHARLIE"
                           2642        2620                260.0

Explanatory Notes

I've used "ABEL", "BAKER", and "CHARLIE", the standard US Army word designations for the letters A, B, and C. This is for simplicity of understanding for those unfamiliar with the territory. For those who want "real" names, the above are based on the PRR Middle Division interlockings PORT, VIEW, and BANKS, respectively.

273.4, 266.4, and 260.0 are the milepost numbers of these 3 interlockings. They are fictitious, and probably too close together for the "average" interlocking spacing in this territory.

I am using |--O to represent a single-arm signal, |--=O to represnt an approach ("distant") signal with a full upper arm and partial lower arm, and |--OO to denote a 2-arm interlocking signal. (If this were color-light signal territory, the distinction between the latter two might, or might not be noticeable to the casual eye.) |-o is a dwarf. |---------| is a signal bridge. Note that signals are to the right (and possibly above) the traffic they control. This rule has only recently been relaxed. (Electrical) track blocks occur at the signal locations; in my experience, these have never been more than a couple of meters away.

Signals for eastward traffic |--O are even-numbered. The number is simply the milepost (including tenths of a mile) times 10, plus or minus 1 in last digit. Westward signals O--| are odd-numbered. Each automatic signal (O--|, |--O, O=--|, or |--=O) would be numbered on the signal mast or on the signal bridge. In speaking or writing, if one needed to be more precise, one would append the track number, thus: "2620-1". But these (track) numbers were not shown on the signal mast/bridge. The presence of a signal number is what identifies the signal as an automatic, as opposed to a controlled (interlocked) signal.

Actually, I must say I like Conrail's system better, which is basically floor(milepost) followed by track number followed by E or W. I.e., where the PRR labeled their maps (and signals) with merely "2620" and "2621", Conrail labels them 2621E, 2622E (for the 2 "2620" signals) and 2623W, 2624W (for the 2 "2621" ones).

Interlocking signals are identified by lever number and R[ight] or L[eft]. These are "never" shown on the signal itself, at least not so that it is in the view of the engineer. In some locations, e.g., in the bowels of Suburban Station, Philadelphia, the back or top of the signal is labelled with its lever number and R or L, presumably for ease of identification for the signal maintainer. In the few locations where interlocked signals are labelled on the front, this fact is noted as a "Signal not in Conformity with the Typical Aspects" portion of the Special Instructions.

On the map, I use a typical US&S numbering scheme, switches odd, signals even. GRS machines had pistol-grip levers with only 2 positions; thus, signals were not numbered in pairs as on US&S machines. The Pennsy had mostly US&S equipment. 2 GRS-equipped towers I can think of offhand are (were) LEWIS and ROCHESTER, in the towns of the same name.

I'm using the PRR track-numbering scheme. PRR numbered its tracks sequentially, from south to north (for E-W trackage), or from east to west (for N-S trackage). The PRR did, on occasion, use "0" (a zero, but generally referred to "naught", or in our Amurikun bastardization, "aught track") or "A" for the 1st track in the series. Tracks were routinely renumbered at larger stations. Some locations added letters, e.g. the "1F" and "2F" Freight bypass tracks at Pennsylvania Station, Baltimore.

The more frequently used scheme (by other railroads) would have tracks 1-2-3 as either 2-1-3, or 4-2-1. 1-2-3-4 would then be 4-2-1-3. Note that this latter system numbers tracks from the inside to the outside, even numbers for eastbound tracks, odd numbers for westbound tracks. This often corresponded to the numbering of eastbound trains with even numbers and westbounders with odd.

Note that #2 track between ABEL and BAKER is bidirectionally signalled, whereas the inner tracks between BAKER and CHARLIE are unidirectionally signalled.

The operator's model board may have the full representation of the interlocking signals, e.g.,

                   o--  |\---
                  / \   | \  
with the signal number and green light alongside it. Or, more frequently, only the green light and the signal number were present. Some boards showed the automatic signals using the scheme above, and the interlocking signals with the green light.

Model boards generally did not have automatic signals shown on them, except for the interlocking's distant signals, and then sometimes not even these. On rare occasions, automatics were significant and were shown. A single set of automatic signals between two otherwise independent interlockings (save for the fact that the 2 were controlled from one location) would often be shown.

Note above I've shown nice, "clean" interlockings, with well defined interlocking limits beginning at the same milepost on all 3 or 4 tracks. This was generally the case west of Harrisburg, but interlocking limits east of there, in the more congested megalopolis that is the US East Coast, got very messy very quickly. One of the bridges over the Susquehanna at Harrisburg, easily a km long, for example, was completely run under Interlocking Rules, one end controlled by LEMO interlocking, the other end by STATE interlocking, with no intervening automatic signals. ROCKVILLE interlocking (the one north of Harrisburg), before its relatively recent resignalling, was notorious for the variety of locations where Interlocking Rules began/ended and Automatic Block System Rules ended/began. The latter interlocking controlled a 4-track main line across a bridge with 2 wyes on either side. In few locations did Interlocking Limits begin on 2 adjacent tracks at the same place.

Interlocking limits are defined by the outermost interlocking signals, often referred to as "home" signals from Manual Block times. In my map above, all of the interlockings are simple and self-contained. More complicated interlockings included additional, intervening, interlocked signals inside the "home" signals. Sometimes these created conceptual "subinterlockings", sometimes not.

Your Mission, Should You Choose To Accept It ...

OK. You're the block operator (tower operator) at BAKER. A train is coming, but you don't know it yet. The sequence of events is as follows:
  1. You have your block line set to the dispatcher, as you should if you're not presently using it. All your switches are set normal, all your signals are set to Stop.

  2. If you're attentive, you'll hear the operator at ABEL call the Dispatcher to inform the latter that the train (its caboose, or last car) has departed ABEL. Note that here, ABEL's interlocking limits are rather short. Were the interlocking limits long, ABEL would have to wait until the train cleared the last "subinterlocking" (was beyond the outermost interlocking signal) before declaring the train "clear".

  3. Buzzer goes off -- it's ABEL calling. His line lights up on your switch panel.
    The switchpanel is a box, say 30cm wide X 20cm high, on your desk, with a row of white lights above a row of toggle switches. Two white lights are now lit, ABEL's, and the Dispatcher's. The last toggle switch on the panel is sprung (momentary-closed) and operates the buzzer. The panel, besides being your "phone switchboard", allows you to set a line "through" your block station, say from ABEL to CHARLIE, which otherwise did not have a direct line. You have additional toggle switches for CHARLIE, the local yard's yardmaster, and others.
  4. You put the Dspr's toggle down to the neutral position and raise the toggle for ABEL, step on the foot pedal, and say "BAKER".

  5. ABEL says: "George, comin' achya [coming at you] on 1 [track] is the [train number] PIOI-46" [he pauses while you write this down on the "Eastbound" section of your block sheet] "the [lead engine number] 7645" [pause] "89 [loads] and 34 [empties]" [pause] "[passed] by here at 10:21".
    The block sheet contains spaces for a number of general items at its top, including Block Station name, date, time, weather conditions, and so forth. The remainder is broken into 2 major columns, "Eastbound" and "Westbound". These are subdivided into 3 columns, the left one for the Block Station before yours (the one west, or east, of you, respectively, depending on the major column), then your Block Station, then the Block Station after yours (east or west, respectively). These minor columns are then further subdivided into columns for train number, engine number (+ additional), loads, empties, and the time the train cleared the given station.
  6. ABEL may then provide any other info, say "I'm expecting [Amtrak] 47 30 minutes late".

  7. BAKER: "OK, Joe, PIOI-46, 7645, 89, 34, 10:21" You repeated the information to show that you received it correctly.

  8. BAKER would now give ABEL any information ABEL needs (see below).

  9. You turn down ABEL's toggle, raise the Dspr's toggle (block line), and wait for the train to arrive.

  10. ABEL's call to you is your authority to clear signal 2R, governing #1 track. We assume here that the Dspr did not call BAKER to instruct you to switch the train over to another track. Note also that "clearing a signal" means "bringing it up" from Stop to something other than Stop, not necessarily to Clear. The circuitry controls this, not the Operator.

  11. If the Dspr had called you to switch the train over to #2 track, you would have to throw switch 1, then throw signal 2R. Messing it up, throwing the wrong lever, would result in you needing to "knock down" the signal. The lever would not move its entire distance, but the signal would show Stop immediately. You'd then turn the 4-minute timer -- this is a safety device, to allow all movements in the interlocking to stop. When this was done running, you could reset the signal lever entirely and bring up another signal. The timer was generally 2 minutes for dwarf signals.

  12. Had the train been coming in on #2 track, ABEL and BAKER would have to have previously (i.e., before the train arrived at ABEL) set both their traffic levers, for that track, appropriately.

  13. While the train is coming toward ABEL, essentially until he passes 2688 signal and enters BAKER's approach block, the train is still under the authority of ABEL. Calls go to ABEL, unless ABEL can't be reached for some reason, when the Engr may call BAKER. Failing that, the Engr may call any tower, or the Dspr, or neighboring railroads' towers, etc.. A westbounder is BAKER's responsibility until passing 2711 signal.

  14. Train arrived in your approach circuit. The bell in the tower rings to let you know of this.

  15. Train comes by you, picking up orders if necessary. You inspect the train as it passes, per the rules. You note the FRED (F**&*^ Rear-End Device) pass your easterly home signal. The train is officially clear of your "[interlocking] plant".

  16. Note that your 2L home signal serves as the block signal not only for the block within your interlocking limits, but also for the Automatic Block Rules block between the limits of your interlocking (the 2L signal in this case) and the following block (automatic) signal, 2642-1.

  17. You sit down, bring up the toggle for CHARLIE, and push down the spring-loaded buzzer toggle 2 or 3 times. You don't get too impatient, as CHARLIE may be talking to the Dspr or to D.

  18. CHARLIE answers "CHARLIE".

  19. You say: "Bob, comin' achya on 1 is the PIOI-46, the 7645, 89 and 34, by here at 10:32" CHARLIE: "OK, George, PIOI-46, 7645, 89 & 34, 10:32".

  20. You write down 10:32 on the "you" section of the block sheet.

  21. You call ABEL and inform him of the train's passing time by you so that ABEL can complete his block record. Once you do, ABEL's responsibility vis-a-vis this train is finished, as he is now informed that the train has left any territory he controls.

  22. You call the Dspr and inform him of the train's passing time. The dispatcher sheet is somewhat simpler than that of the each tower, but it is also much longer (left to right). The dispatcher writes down the train name once, then writes a sequence of times of when each train passes each station over which the Dspr has jurisdiction. In this case, your Dspr is sitting in an office, with no view of any train, some 200 km away.

  23. You restore your signal lever to neutral position [the signal has, of course, remained at Stop since the train passed it and tripped the block detector within the interlocking]. You restore any switch levers thrown reverse to normal position.

  24. The train remains under your jurisdiction until he reaches CHARLIE's approach circuit.

  25. Eventually CHARLIE will call you and give you the train's time passing CHARLIE, which you will write down in the 3rd subcolumn of the Eastward column. This makes complete your record for this train, i.e., its number, engine number, consist, and 3 times, for ABEL, BAKER, and CHARLIE.

If you make an error ...

If you realize you set a route in error, the following procedure was followed:
  1. You will "knock down" the signal. How is this implemented? On US&S interlocking machines, the op must turn the knob on the end of the signal lever to allow it to move, but then it will move only about 10-20% of its normal excursion toward the central, neutral position. (The signal levers rotate right or left by a total of about 40 or 50 degrees of arc.) This is enough to "knock it down" but not enough to unlock the signal or affected switches.

  2. The Op must set the timer before regaining control of affected portions of the interlocking machine. Some towers that had "subdividable" trackage would have more than one timer. In nearly all cases, though, there were 2 timers, a long one (say, about 4 min) for high signals, and a short one (say, 2 minutes) for dwarf signals. The exact time ("4 min 20 sec") was noted next the a white lamp on the model board which was lit while the countdown was in progress.

    The time was also marked on the timer. Timers had rounded cylindrical glass domes with the knob on the dome face.

  3. When the timer expired, the op could move the signal lever back to neutral (remember that US&S machines had "R" and "L" settings controlling separate signals, the signals usually facing opposite ways on the same track).

  4. Once the signal leer was back to neutral, the affected switches became unlocked.

  5. You could now set the new route. Hopefully the train did not have even to see a yellow signal at your distant.
There was also the tower horn. The PRR rulebook specifies a single, LONG blast of the tower horn to be an indication for all movements within the interlocking to stop. I saw this used once when a passenger train was about to leave Lancaster station without orders -- there was a maintainer on the ground about a mile away at the Conestoga R. bridge and there being no intervening signals between the train and the maintainer. This tower (CORK) actually had 3 horns, because of the length of the interlocking (several miles).

Additional tower horn signals were for warning ground personnel, etc.. Plus trains occasionally received orders to blow their horn frequently for maintainers' safety.

Other Duties

The curious may also be interested in reviewing the duties of operators, levermen, etc. as listed in the PRR Book of Rules available on this site. Rules referring to operators' duties are scattered throughout the rulebook.

Jon Roma has written, as well, on the relationship between jobs of various people working in interlocking towers. The following was penned 1996.01.26 and presented in [relevant] part.

I think I have noted this in the past, but it's an interesting contrast between U. S. and U. K. practice as to the breakdown of duties between the various men working a tower/signal box. In U. S. towers staffed by more than one employee, the higher paying job is that of the operator (often referred to as the train director where local conditions give him operating authority over an area beyond simple interlocking limits). This job is universally held by an employee more senior than the levermen. His responsibilities include communicating with adjacent towers, stationmaster, notifying by telegraph or telephone the dispatcher of train movements, keeping the station record of train movement (a.k.a. the train sheet) and determining moves and calling them to the levermen. The operator would handle train orders in towers where train order work was done. This job, while mentally demanding, can be conducted largely from a sitting position and without any great degree of physical activity.

The levermen, on the other hand, are on their feet during a large part of their work day and fundamentally do nothing more than pull levers for their eight hour shift. Though a certain degree of mental agility is required to expedite train moves, the decisions are made by the operator/ train director and the levermen exist to tussle with the levers.

As I understand it in the U. K., the booking boy keeps the record of trains, freeing the signalman to handle most of the communication between boxes and make decisions with respect to train movements and to move the levers himself to suit. So most of the hard work -- both mental and physical -- are vested in the signalman if I am understanding and recalling U. K. practice correctly.

Mark D. Bej, M.D.