ACL Cab Signals (ATS?) : LUSENET : ACL and SAL Railroads Historical Society : One Thread

I noted a reference to "Cab Signals" in a 1950 copy of the ACL Operating Rule Book. I have also noticed what appears to be ATS pick-up shoes in a number of photographs of ACL locomotives. I am guessing that the ACL Rule Book reference to Cab Signals was ATS (Intermittent Inductive Automatic Train Stop) as opposed to Cab Signal (Continously Coded Cab Signals.) Am I guessing correctly? I am also curious as to what portions of the railroad were equipped and between what approximate dates. Further... Did any of the ACL power have RF&P Cab Signals for run though or did they simply operate on-line unequipped. By the time that I started paying attention to dispatchments south of Washington (Amtrak in the late 70s) we were concerned only with RF&P compatable cab signals. Thanks in advance for any info.

-- Clifford P. Kendall (, August 22, 2000


Thank you Mr. Morton for clarifying that point. I was remiss in not clearly stating that the inductor was not connected to a source of energy-the sideline that appeared on the web site on "How Train Stop and Train Control Systems Work" did not clearly state that-for that I apologize and I appreciate your clarification.

-- Michael W. Savchak (, March 03, 2003.

In an atempt to make this an accurate record of ACL Train Stop Equipment it must be stated that ATS Inductors were ineret devices with no energy in the inductor, and were never magnetized to provide for acknowledgement at all times. The inductor has two pole pieces that corespond to the distance between the primary & secondary pole pieces on the locomotive receiver. Between the pole pieces on the inductor is wound a choke coil that is opened or close by the Front Contact on the 'D' Relay at each fixed signal location. The choke coil is only closed when a fixed signal displays Clear/Proceed; at all other times it is open and requires the Inductor to be Acknowledged for the Engineer to retain control of the Automatic Brake. Simply: when the signal is restrictive the inductor choke coil is open, and the inductor produces a flux change in the receiver on the locomotive which must be acknowledged. When the signal is clear, the inductor choke coil is closed, and the flux change produced in the locomotive receiver is not sufficient to make acknowledgement necessary.

Note the transmission of control between the inductor and receiver requires NO ENERGY in the inductor winding.

It was the practice on the ACL at locations where it was desirable to require acknowledgement at all times to use what amounted to an unwound inductor with no choke coil. This device was simply a piece of strap iron identical to the dimensions of an inductor and bolted to the ties. Account not having a choke coil that could be closed it always produced a flux change in the locomotive receiver that required acknowledgement. It was standard practice to have two of these strap iron inductors placed one ahead of the other in the outbound lead from an Enginehouse or Hostlers Yard. When taking charge of a locomotive the Engineer was required to acknowledge the first open inductor when departing the Hostlers Yard and not to acknowledge the second open inductor causing a penalty application of the Automatic Brake. This was the test that qualified the equipment for service and a suitable entry was made on the work report for the lead unit that allowed the ATS equipment to remain in service for 24 hours or one calendar day.

This information is late to this forum but furnished to make an accurate account for history of a device that is no longer in service.

-- JR Morton (, February 28, 2003.

Buddy Hill asked about the different types of train stop receivers seen on the ACL steam engines. As a result of my research for an up- coming Lines South article, I have been able to solve the mystery.

The General Railway Signal Company supplied the ACL with two types of engine mounted train stop receiver. One was an inverted "V" shaped unit called a Schedule 1 receiver. It operated on 2.2 amperes 32 volts DC and was mounted such that there was 2 inches clearance above the wayside inductor. The other type of receiver was a rectangular unit called a Schedule 2 receiver. It operated on 3 amperes 32 volts DC and was initially mounted 1 1/2 inches above the wayside inductor. Eventually, the ACL phased out the use of the Schedule 1 receivers and used only the Schedule 2 apparatus. Other roads using Schedule 1 apparatus were the B&O, D&H, LV, Pere Marquette and Southern.

Both types of apparatus were used on the ACL, but the Schedule 1 apparatus was found to be a little too sensitive and was replaced by Schedule 2 apparatus on all roads.

-- Michael W. Savchak (, August 06, 2002.

I would like to thank everyone who answered this question.I think it is one of the most informative questions(and answers) ever asked on this site.Great work! Keep it coming.

-- J Oates (jlosal@, August 31, 2000.

Diesel Spotting Features ACL E's with Cab Signals:

Look for square box mounted on center journal box rear truck left side of locomotive. This is the speed govoner necessary for Cab Signal Operation on RF&P. Seem to recall we had 17 units equipped (does anyone know the unit numbers???) all were low numbered 500's can't remember any E-7's with Cab Signals.

Diesel Spotting Features ACL Units with ATS:

F Units had Receiver mounted on first journal box right front truck E Units had Receiver mounted on last journal box right front truck

-- JR Morton (, August 30, 2000.

Buddy-good question! I will have to go back into the early literature from GRS and US&S and look at their respective offerings. Most Intermittent Inductive Train Control systems were sold by GRS, other railroads such as the New York Central used this system extensively. In fact, the GRS literature shows the pick up mounted on a NYC diesel.

At this point, I would probably lean toward the bell shaped device as being an early version of the receiver which was later changed to give a better ability for pick up.

Incidently, some of the old timers here at Metro-North remember the NYC system as being subject to false applications due to magnetized scrap along the tracks. Now that is typical-track department leaving their scrap along the tracks and then listening to the signal guys complaining!

-- Michael W. Savchak (Savchak, August 30, 2000.

To comply with ICC's mandate that one division be equipped with cab signals, automatic train stop, or automatic train control, N&W chose the Shenandoah Division for its applica- tion. N&W also supplied power for the "Short Runs" -- the shuttle service ACL provided between Broad Street Station and Appomattox Street at Petersburg. N&W 4-8-2's Nos. 121-122-123 were fitted with ATS equipment compatible with ACL's. In ACL service, these engines were 160-plus miles away from the closest N&W installation.

-- Harry Bundy (, August 30, 2000.

Interesting reading - the information presented so far would definitely make a great "nuts & bolts" type article. I've got a question regarding the application of ATS to ACL steam locomotives. A review of ACL steam photos indicates that there appear to have been two styles of ATS pick-up shoes in use. The first style of pick up shoe was a "U" shaped device and was applied to both steam and diesels as referenced in the above responses. Other photos show a different device that appears to have a flattened bell shape and was placed beneath the tender on the engineer's side and immediately to the rear of the lead tender truck. Are these different versions of the same device? Are they from different manufacturers? Any information would be appreciated. Thanks.

-- Buddy Hill (, August 30, 2000.

For all those who followed this discussion, I have an old GRS book which has a section on the intermittent inductive train control system. If you are interested, send me an E-mail with your snail mail address and I will send you a copy of the pertinent section.

-- Michael W. Savchak (Savchak, August 30, 2000.

Thank you Mr. Morton!!! Now it all makes sense. Because the two systems were so different, dual equipped units would have been the only way that through runs with out speed restrictions could be possible. This also has a bearing as to why SAL power did not run north of Richmond-they were not cab signal equipped.

Based upon the available facts from everyone who conributed, it appears as if RF&P initially had a simple cab signal/train stop system utilizing inductor technology similar to the ACL's in the pre- war period. Post war, ACL stayed with its intermittent inductor train stop system, while the RF&P updated its system with a continuous coded system. When through running of power was established in 1964, both RF&P and ACL dual equipped some units.

Now-when was the ACL's train stop system disconnected? Were any ex SAL units equipped with ACL train stop or was the train stop system disconnected prior to the merger?

As for Cutis Denmark's statement about two types of inductors, the permanently magnetized units were primarily used as "alertors" to ensure that enginemen were alert, especially when approaching areas where there were permanent speed restrictions, such as drawbridges, etc.

Again, thanks to everyone for providing the clues to solve this puzzle!

-- Michael W. Savchak (Savchak, August 30, 2000.

I'd be remiss if I didn't also mention that some mighty capable people are what made things like the above posting possible. The RF&P units modified for ACL run-thru service were done at Bryan Park under the direction of a real southern gentelman Mr. W.T. (Bill) Rainey the CMO for the RF&P. ACL units were done at Florence by General Foreman J.C. Rodgers who was the "spark plug" that kept those 500's servicable. When it came to an E unit, J.C. was the origional "been there, done that." There was nothing that could happen to those old E's that JC couldn't tell you how to fix or overcome to make the engine run. After beeing in engine service now more than 30 years I am reminded of the old saying; "they serve who also stand and wait." JC was that kind, he made things happen so we could make a mile up the 'short cut' in 36seconds with #92.

-- JR Morton (, August 29, 2000.

Reference ACL units operating on the RF&P with RF&P Cab Signal Equipment. Some number of 500's (I beleive 17) were equipped with both ACL Interemitent Inductive Train Stop (Receiver located on rear journal of front right truck) & RF&P Continuious Train Control (pair of coils suspended 4" above each running rail immediately behind pilot of locomotive). There was a change over switch mounted on the back wall of the nose of the locomotive on the left (firemans) side. This switch was manufactured by GRS and was labled "ACL" & "RF&P". A brass handle on top was positioned over the cast letters on the box to reflect if ATS or Cab Signals were operative. This change over was made at Broad Street: northbound trains stopped over a test loop that ran a sequence of tests to cause the cab signals to display all aspects. This test was run twice; the 1st time each time the cab signal fell to a more restrictive aspect it was acknowledged, the second test the cab signal went from clear to restricting and weas not acknowledged causing the brakes to be applied. Thes two test qualified the unit to be in the lead operating over the RF&P to Ivy City. Southbound the Cab Signals were cut out and the ATS cut in. Two tests were also made to qualify the equipment to go south on the Coast Line. One test would have an electrician pass an iron bar under the train stop receiver and when the cab whistle sounded the engineman would acknowledge. The second test would not be acknowledged and hence the automatic brake would be appled with a penalty application. I do not have information to accurately state how many ACL 500's in run-thru service had Cab Signals (I think 17) but my notes from 1966 indicate that four RF&P E-8's (1012-1015) in addition to having a front end jumper recpticle for operation on the Coast Line had ACL Train Stop. RF&P units 1010-1011 had the nose mu only so they came south on us to run off excess mileage on the Coast Line when the RF&P was indebt to us (milage was adjusted each month and equalized) but these uniots could only train on the ACL account not having ATS.

-- JR Morton (, August 29, 2000.

ACL locomotives used in main line service were equipped with ATS. This being a device that interacted between the locomotive and a wayside signal to ensure that an engineman "acknowledged" a restrictive signal. A wayside "inductor" located approximately an engine length in advance of a wayside signal was an iron ple piece with two coils wound on it. These two coils were connected thru a relay at the signal when the signal displayed a Clear Indication; any other indication than clear and the relay was down allowing the connection between the coils to be open. When the receiver on the locomotive (that also contained two pole pieces) passed over an open inductor a bucking voltage was induced in the ATS equipment on the engine dropping out the R-1 Relay and causing a penalty application of the brakes. This could be prevented (called forestalled) if the engineman operated an acknowledging lever located adjacent to and on the right inside cab wall next to his seat. This lever picked up the R-3 relay in the ATS equipment which was a shunt around the R-1 Relay and prevented a penalty application of the automatic air brake at those signals that required they be acknowledged (all execpt clear). The R-3 had a timing mechanicism on it so that it could not be held up continuiously and thereby defeat its purpose of acknowledging; so the process was to acknowledge as the receiver on the locomotive passed over the open inductor. A three chime whistle operated from an ATS Magnet Valve would sound momentairly to indicate that the restrictive signal was acknowledged. If not properly acknowledged, this three chime whistle was a choke in the #10 Application Pipe that caused air to be vented to atmosphere and this in turn is what initiated the penelaty application of the automatic brake.

-- JR Morton (, August 29, 2000.

For what it is worth, I will contribute the following information. I was an Assistant Signalman on one of the ACL, Signal Gangs 1960-1963. For a good bit of that time, we were one of the two gangs that were involved with the single tracking project from Rocky Mount, South.

At the time I was a young buck that was primarily on the "Bull Gang." Lifting, digging, painting, and toteing things versus wiring of the technical stuff.

The large inductors that spanned several cross ties were of two varieties. Some had wires and were electrically active. Others were without any wiring and just a plain inductor. The information I was given, was that the plain ones activated a device in the engine that the engineer had to acknowledge.

In other words, it was an engineers warning of the presence of a wayside signal. It did not give any cab aspects of the wayside signal, just that the searchlight signal was out there. Regardless of the aspect, the engineer merely acknowledged to the in cab device, that he could see the signal.

If he did not acknowledge the presence of the signal the train would go into a braking mode. Perhaps a simple system to comply with the ICC requirements. The locomotive pickup was on the engineers side axle.

I can only attest that they were heavy and required us to use a large brace and bit (armstrong) to bore though the ties for the mounting bolts. Also, had to dig out under the ties to fasten the nut to the bolts. There wasn't much of anything easy about this work.

Sorry I couldn't tell you more, but hope this tidbit of information might help.


-- Curtis E. Denmark Jr. (, August 29, 2000.

You may be right. Now I am going to have to look for thar cab signal table and see which one it was. I think I brought a copy home. The problem is that most of the old buff files are still in boxes after the move. This may take a while gang.....

-- Clifford P. Kendall (, August 29, 2000.

Interesting-would the difference be the code rate-i.e. 75-120 or 180 code? RF&P probably used a 60 hertz carrier while PRR used 100 hertz. The reason for the higher frequency was to eliminate the possibility of traction current interference. 100 hertz is the fourth harmonic of 25 hertz and the fourth harmonic is always one of the low harmonics.

-- Michael W. Savchak (Savchak, August 29, 2000.

Hello Harry, Sounds like the RF&P may have started out with one of the many ATS variants and later switched over to continously coded cab signals. Dual equipped locomotives (ATS and continously coded cab signals are very different animals sharing very few componets, as you know) I would think, in that day would have been prohibitively expensive. As for the reroute trains, I suspect that they had an RF&P leader assigned. In a somewhat related story... I remember (when I was at Amtrak) getting a call from Conrail inquiring about the code frequencies for the RF&P cab signal system. They wanted to add RF&P cabs to their Executive E8s so that they could lead on the RF&P. RF&P has a few different "cycles" than the Conrail exPRR. Somewhere in my stacks of paper I may still even have the answer. Thanks for another piece of the puzzle.

-- Clifford P. Kendall (, August 29, 2000.

As they say, the plot thickens! When writing the earlier answer, I had forgotten about the short period of time in the late 1930's-early 1940's when SAL engines ran through to Ivy City and used the RF&P. Logic compells me to state that the units were equipped with RF&P compatible cab signals. The easiest course of action would be to get an RF&P employees timetable for say 1965 and see which units they permit to operate as the lead engine-and then to see the same for the ACL.

Unfortunately, I am not a signalling guru-I did dabble some but am not an expert. The two types of system are different. Cab signals just repeat the wayside indications in the cab. A train control system may be coupled with cab signals or not. Most intermittent inductive train stop systems had a whistle which sounded when a signal was at restricting. The railroad's rule book would provide the necessary information on which system it had and how it worked.

So-anyone out there with an ACL and RF&P rule book (say 1965) which they can share with me-then maybe I can answer the question with accuracy.

I gave my RF&P and ACL employee timetables to the Society last year. Maybe Larry G. can retrieve them (after he finishes the AB&C book!) and I can dig through them to see what they may have to say. They were dated 1961-62-63. Who knows-maybe a future Lines South article. Anyone willing to co-author?

-- Michael W. Savchak (Savchak, August 29, 2000.

Apparently at one time ACL passenger diesels had ATS compatible with RF&P's system. During World War II, ACL's E units regularly operated between Richmond and Ivy City, D.C. via RF&P. RF&P's Time Table No. 97 eff. July 9, 1944 indicates RF&P had cab signals capable of displaying Green, Yellow, and Red. By 1952, RF&P had started adding coded track circuits and coded train control (and ACL units no longer went through to Ivy City). What happened after that seems to invite more questions. During August and September, 1969, how did Southern trains detouring via Raleigh-SCL-Richmond-RF&P cope with RF&P's signal system ? (I did see two RF&P covered wagons leading Southern units with a freight).

-- Harry Bundy (, August 29, 2000.

The ACL system was as you correctly inferred, an Intermittent Inductive Automatic Train Stop system. Initially, the railroad was equipped with such a system following the ICC's 1920's requirement that at least one division of each railroad be equipped with a train stop, train control or cab signal system. The line between Richmond and Florence was then equipped. Following the ICC's June 17, 1947 order limiting train speeds to 79 mph unless such systems were in place, the ACL started to install the train stop system south of Florence to jacksonville, completing it in 1955. This then permitted the ACl to start a short lived 100 mph operation. Prior to that time and the ICC 1947 order, maximum speed limits were 90 mph for diesel, 70-75 mph for steam. Of course these speed limits were often exceeded, and contributed in part to some accidents-i.e. Fleming GA Jan 17, 1953.

I am not 100% sure if all ACL units had RF&P compatible cab signals- but running as an unequipped unit results in serious operating restrictions that tend to tie up a busy railroad like the RF&P, so that it is a good possibility that the units did have systems compatible with the RF&P. RF&P units began running on ACL trains south of Richmond as a result of a 1964 run through agreement. Perhaps Harry Bundy might shed some light on this.

-- Michael W. Savchak (Savchak, August 28, 2000.

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