Data Infrastructure Increasingly Substitutes for Radio Comms

I have been reading reports that as PTC systems are being certified for operation, their data transmission facilities are being used to transmit various mandatory directives such as Track Warrants, Temporary Speed Restrictions and Work Limits. Moreover, company issued electronic devices are also being used to send the same type of "paperwork" in various electronic formats. Previously read over open channel VHF radio to be copied and repeated by the crews, the new methods keeps the information off the air with the radio link only being used to confirm delivery.

 

Although a loss for the scanner community, delivery of what I will call "train orders" has used closed communications channels since the first telegraph line was established to replace a pure timetable system. Hand and telephone delivery have always represented a small, but durable portion of train order transmission since radio communications became a thing in the 1970's. Closed communications channels have long been the norm in Europe using a dedicated GSM-R band set up for the purpose.

I would still anticipate policies on train order transmission to evolve as one of the greatest benefits of open channel communications is the situational awareness provided to all manner of right of way workers and train crews who may wind up at the wrong place at the wrong time. There are countless stories of accidents averted because someone was tipped off to an unsafe situation through radio chatter and is also one of the reasons signal calling remains a thing.

It will be also interesting to see how the scanner community adapts and if PTC deciding will become a thing like ATCS decoding. Although not as open as analogue VHF, there are no FRA requirements to encrypt PTC data, only requirements to authenticate safety critical data. What the industry has decided to do remains to be determined, but with locomotives needing to be able to operate across the national network it is highly likely that industry will seek to minimize the certificate management problems. It is also likely they will just do a bad job resulting in security that is easily exploitable.

Exit Stage Right - Leaving Signaled Territory

Typically I write about railroad signaling, occasionally touching on non-signaled block systems such as TWC or DTC.  Each are more or less straightforward on their own, but things can get interesting when transitioning from one to another, specifically from signaled territory to non-signaled territory.   the three primary methods are:

1. Exiting at a Manual Block signal
2. Exiting over Restricting
3. Exiting at a sign

Although some of these have a few additional complexities that I will go into below.

WINSLOW Jct on the PRSL had two exits into Manual Block territory.

 Under mostly defunct manual block systems, trains would be admitted to the block by a manual block signal, typically under a modified Clear indication like Rule 280 Clear Block in the PRR Rule book.  These signals would be located at the start of manual block territory directly after the interlocking or on the last signal on a route that could lead to manual block territory.  A signal less favorable than Clear Block would be preceded by an Approach-type indication.

NORAC Rule 290 Restricting into DCS territory.

With the coming of Track Warrant systems like Conrain's Form D Control system (DCS), trains moving from signaled territory to DCS territory would be given a Restricting indication, regardless of the trains DCS movement authority.  In fact this method of operation was written into the text of NORAC Rule 290.

Proceed at Restricted Speed until the entire train has cleared all interlocking and spring switches (if signal is an interlocking or CP Signal) and the leading wheels have:

1. Passed a more favorable fixed signal, or
2. Entered non-signalled DCS territory

 This is also the standard when trains are moving into a yard or non-signaled sidings, although in those situations the train is entering Restricted speed track as opposed to a non-signaled block system.

Seaboard Rule 290 Restricting into Collier Yard.

In addition to placing the Restricting signal at the entrance of the interlocking, it can be placed on an exit signal allowing higher speeds throughout interlocking limits.

Exiting at a sign means that signaled territory ends at a sign instead of a signal.  This can be used with signaled approach blocks to allow reverse direction trains to occupy the approach block without needing to get a track warrant, as seen below on the old D&H near Saratoga Springs, NY.

 

Where signaled approach blocks are not present, the exit sign can be used at the end of interlocking limits.  As with the Restricting exit signal, this allows a more favorable indication, such as Approach or Slow Approach, to be displayed at the start of the interlocking.  This in turn allows higher speeds for pretty much the cost of a sign and also better supports non-restricted speed track as, unlike the Restricting signal, Restricted speed is not necessarily required if the train possesses non-signaled movement authority.

NJT ARCH interlocking eastbound home signal.

Recently a more radical take on the exit sign has started cropping up.  Instead of treating the signal as a virtual restricting signal demanding an Approach-class signal in advance, some railroads, including Norfolk Southern, have been configuring their interlockings to display Clear-class signals into an end of signaling sign, even if that sign is located at the interlocking limits.

For example, at CP-PORTER, shown above, the main track signal displays Approach for a straight route towards Restricted speed track marked by a sign at CP-PLANT.  However it also can display Slow Clear for the diverging route directly into a Track Warrant territory (Rule 171) sign at CP-PORTER's southern limit.   The only other option is Restricting if the route is occupied within the interlocking itself.

Trains being signaled into Yard Limits directly north of CP-PORTER get an Approach-class signal on the straight route, but a Slow Clear on the northeast wye track.  While all this inconsistency can technically be considered safe as the signs technically overrule the preceding Clear-class signal.  Still, I am not a fan of this practice as it is important to never violate the contract that a Clear-class signal provides two clear blocks ahead and an Approach-class one clear block.  Unless approach blocks are being used, a signaling system has no idea about the state of the track in unsignaled territory and a Clear-class signal would be writing a check the signaling system cannot guarantee.

Conflicting Route Conundrum

So the following photo drew a number of questions on both its own page and also a few of the signaling forums.  As one can see it appears that two conflicting routes have been lined over the same switch at the end of a passing siding, something that appears to indicate some sort of failure in the interlocking, or some photographic trick like multiple exposures.  The photo was taken on a Norfolk Southern line in Georgia and it's location is one reason that people are so confused.

Before I give away the answer I'll first state that the signaling logic is functioning as intended and there was been no photographic trickery.  Still, Clear and Diverging Clear appearing next to eachother in this context should be contradictory.  Here's I'm going to post another photo from a different part of the country that is a pretty big hint about what's going on here.

This was taken on the former ATSF Raton pass line where the last operational semaphores in North America are located. These semaphores are constantly being photographed, but nobody seems to be confused as to why adjacent signals can both display clear like this.  Well, there are two reasons.  The first is that there is something about Diverging Clear sitting next to a Clear at the end of a siding that just seems plain wrong.  The other reason is because the sort of signaling where this circumstance occurs is much more common out west than it is in the east.

This is your last hint before I give away the answer/

 If you haven't figured it out yet the answer to the puzzle is that the signals in both these pictures do not protect an interlocking and are not part of a CTC setup.  They are part of an ABS-TWC (aka NS Rule 271) arrangement, that also likely an example of Automatic Permissive Block .  The signals operate automatically based on occupancy of the line ahead and, more importantly for this post, trains exiting the siding do so over a spring switch so both routes through the control point are valid.

Surprise!  It's a spring switch and its also not an interlocking.

ABS-TWC / Rule 271 can actually take a couple of forms.  The first involves signals placed only on the main track so trains on the main and the siding will encounter the same signal and act accordingly.  The other places signals on both the siding and the main.  Since they are operating automatically and they 'protect" a trailing spring switch, both signals will default to a Clear indication.  Out west if there is only one possible route from a signal then the railroads don't bother with a lower head since they are happy to have route signaling handle the switch speed through the timetable.  However in the east it is standard practice to provide reduced speed movements with a  Diverging or Reduced Speed Clear signal indication.

Same situation, one less signal.

 This arrangement is not always an example of APB because APB involves an element of traffic control with absolute headblock signals that prevent trains from entering a line segment where an opposing movement is under way.  Typically the presence of absolute signals at siding exits implies APB, but this is not always the case and NS Rule 271 operation requires Track Warrants for traffic control.  In theory an APB line can operate under Rule 261 with the Conrail Southern Tier Line being one example

Well, what's enough of me rambling on.  Like I said this arrangement is far more common out west and there you don't see the Diverging aspect.  This is why it is absolutely critical to have a good understanding of how traffic control applies to various methods of signaling.  Realizing the line was running under Rule 271 with manual traffic control, it is clear how two trains could never take both routes simultaneously.

CSX: Where TWC and DTC Collide

Like most North American Class 1 railroads CSX is an amalgamation of various predecessors. Not only are there the Seaboard and Chessie System components (themselves the result of mergers), but the former Conrail and Louisville and Nashville territories and several smaller lines such as the Rechmond, Fredericksburg and Potomac and Monon. Each were incorporated with their own rulebooks and signaling practices and until recently CSX continued to maintain multiple rulebooks across its network. In 2007 CSX switched to a brand new unified rulebook, but in order to avoid any drastic change in operating practices many of the previous flavours of rules were simply combined into a single document. Apart from the signal rules (which have sections for Chessie, Conrail and Seaboard aspect systems) the section which most heavily reflects this sort of conglomeration is the one concerning Track Warrant Control (section 5, page 9, if you want to follow along.)

Before the Conrail merger in 1999 CSX used Direct traffic control on all of its unsignaled lines. DTC makes use of fixed blocks with movement authority provided from the dispatcher to the train directly via radio communications (hence the D in DTC). This was in contrast to previous systems where trains would follow a predetermined timetable and any changes would have to be given to crews via block operators or lineside telephones (aka Indirect Traffic Control). When Conrail trritory was incorporated those lines used the Form D Control System or DCS. This was similar to DTC it referenced stations and interlockings as valid block limits (with a block limit sign being a form of station), but don't let the D in DCS fool you as DCS is a Track Warrant system, not a DTC system.  Track Warrant Control not only allows for movement authorities to be given between traditional block limits, but also to any whole milepost or switch.  Moreover Track Warrants can be used for other things besides train movement authority and usually end up combining several forms, like speed restriction updates, into one. While in theory this could have just meant a change in paperwork, mucking about with safety critical systems takes care so CSX decided to make the new TWC system backwards compatible with the old and therefore split it's new TWC rules int two sub-sections TWC-DTC and TWC-DCS to accommodate the differences between the original DTC and DCS systems.

While TWC is more versatile, DTC is simpler and more efficient at doing the things it does.  Instead of trains needing to write out new or amended track warrants, DTC blocks cab be released as they are cleared and then immediately given to other trains. Still, it is clear that CSX's preference lays with the TWC-DCS rules as they immediately went about ripping out all of the old DTC block signs wherever it was most practical like on signaled main lines where DTC used to substitute during signal outages.  DTC references were also largely removed from the employee timetables indicating that the sign removal wasn't just a cosmetic change.  Still, there remain a few locations where DTC remains in effect, mostly on unsignaled secondary lines where use of DTC is more efficient than having crews fill out full Form D's.

Say Goodbye to old CSX DTC Block Signs Like These

Where DTC will be most difficult to dislodge is in the circumstance of bi-directional ABS without traffic control, known under NS as Rule 271 or out west as TWC-ABS.  One might see bi-directional automatic block signals as an indication that a line as been equipped with CTC. However as spelled out in its name, CTC is a system for Traffic Control, not block separation. Traffic control means that when a train is given a route into CTC territory a flow of traffic is established such that opposing movements are not permitted to enter that line. Failure to establish a flow of traffic can result in Mexican standoffs away from passing points or certain race conditions that can cause a head on colision. Because CTC requires logic beyond simple automatic block occupancy to establish a traffic flow back in the day it was more than some lines wanted to deal with. However the advantages of ABS with its broken rail, hand switch point detection and flexibility for following movements could not be ignored. While not common on CSX it does appear occasionally, with the former Monon Railroad main line being perhaps the best known example with the line retaining the same system of operation even after the semaphores were removed.  The new system, known as TWC-DTC (ABS) (!) is at least slightly more clear than the old Rule "120-132 (243-246)" label. 

To accommodate both its traditional and signaled flavors, there are several types of DTC block authorities that can be given. The first is Absolute Block, which has the standard definition, but allows trains with such authority free use of the block in both directions. The next is Clear Block. This grants authority in a single direction guaranteeing the block free of obstructions, but allows say a train in a siding to proceed in the opposite direction on its own DTC authority once passed by the conflicting movement. The third is Occupied Block, which like the name implies allows a train into a block with an obstruction. This is not intended to be used for permissive operation, only the case where one train needs to assist another or pickup equipment left unattended on the tracks. Finally there is a fourth type of DTC permission, Proceed Block. This grants trains the authority to proceed governed by fixed signal indication. This is the only type of authority given in TWC-DTC (ABS) blocks and this rule unlocked the mystery of why such a system exists in the first place back when I first encountered it several years ago.  While all other railroads use full length Track Warrants on bi-directional ABS territory CSX has allowed this situation to remain the province of DTC even as DTC is abandoned elsewhere.