A blog devoted to explaining the ins and outs of North American railroad signaling, past, present and future. This blog seeks to preserve through photo documentation the great diversity and technical ingenuity of 20th century signaling and interlocking hardware and technology. Related topics cover interlocking towers and railroad communications infrastructure.
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The Approach Restricting signal indication has a bit of a bad reputation in the land of speed signaling east of the Mississippi. Typically, the signal progression in both the NORAC and CSX codes are Approach -> Restricting with the idea being that since Restricting could be displayed with an obstruction 5 feet inside the signal, there is no benefit to preparing the engineer to do anything other than stop. Yes, NORAC does have an "Approach Restricting" rule, but it's basically a re-branded distant Approach or PRR Caution signal that doesn't really capture the spirit of approaching a signal in block signaled territory and finding the next signal displaying a Restricting indication.
Calling this "Approach Restricting" is an insult to "Approach Restricting"
So the real Approach Restricting is found in route signaled territory both in the west and on the Southern. Now I know that you are thinking that "Restricting" implies a speed, but the rationale behind Approach Restricting is much more apparent in a route signaled context. Below is the true meaning of Approach Restricting, caught on camera.
Y/L Approach Restricting leads yo...
R/Y Restricting for a route into a siding.
The traditional use of Approach Restricting was as a route indication to alert trains that they had been routed into a non-circuited (Restricted speed) siding. This was popular out west because there Single Track with Passing Siding was the predominant form of rail line. Once CTC started being installed it was logical to distinguish a movement into a signaled siding (Approach Diverging) from a non-signaled track (Approach Restricting) from some sort of regular Stop or Stop and Proceed signal (Approach). However, as speed signaling has started to gain traction on western roads, signal engineers and consultants have started employing it a wider variety of situations.
Ok, tk1 has a route lined at the next interlocking and tk 2 does not. Is this distinction really going to make a different here?
For example on the CN Waukesha Sub (METRA North Central line), Approach Restricting was widely applied as a capacity improvement, although as eastern railroaders pointed out, it's unclear how much one actually gains from this unless one is bending the rules of being able to stop within 1/2 vision. Approach Restricting (and Medium Approach Restricting) has also showed up on the hyper speed signaled Caltrain line, right along side Approach Slow.
Y/*R* Approach Restricting
This of course brings up the alternate Approach Restricting aspect, Y/*R*, which of course has become popular as *R* took over for Lunar for Restricting (since using 4-lamp monster heads is just wacky *cough*CSX*couch*). Since many two headed distant signals use placeholder Reds, this has made all of them a potential location to employ Approach Restricting. In fact, when the aforementioned CN Waukesha Sub was re-re-signaled, Y/*R* Approach Restricting came in to replace the lunars. You can see an example of "speed" style Approach Restricting on the following video montage of flashing signals on the Waukesha Sub (cut to time code 00:23).
Well I hope this sheds some light into the past, present and future of the Approach Restricting indication.
Today I hit the jackpot as part of a Philly area rail transit trip I help organize. While riding a short turn on SEPTA's Fox Chase line, I happened to catch a student engineer being instructed on how to operate a set of new Silverliner V cars and also deal with the new ACSES PTC system. Because of the glorious half cabs, the instructor was sitting in the second seat row and the student had the cab door open. From there I had a mostly unobstructed view into the cab where I could video the cab signal/ACSES display unit and how it behaved.
Until now, how ACSES would function in service was mostly speculation. Although Amtrak has had it in service for 15 years now, there have been few reports (and no video) of the system from an Engineers point of view. This made me optimistic that any impact would be minor and mostly involve positive stop points at stations. Of course there is wide variation and little regulation regarding how ACSES (and all other PTC systems) are implemented from a human factors perspective. There is also a fair bit of wiggle room in how the speed and stop enforcement take place with a good deal of it being policy decisions by railroad management, not necessarily the FRA or other third party safety scolds.
What I discovered today hit on both of these points, and neither fr the better. Note that the observations below apply only to SEPTA andwhat they saw fit to require of their vendors and signaling department. I know for a fact that similar railroads are examining other options. Hopefully if anyone involved in other projects they will take away some things to avoid.
Captured below are two runs on the Fox Chase Line from NEWTOWN JCT to the end of the line in Fox Chase and back. ACSES is in service on the entire Fox Chase Line NEWTOWN JCT excluded. The second video has a better angle on the cab display unit. Station stops were omitted and a few ACES / CSS changes were lost.
As you can see, the SEPTA ACSES system communicates the braking curve to the engineer by means of an Authorized Speed countdown system. As a speed restriction approaches the ACSES speed will begin to drop. If the train's speed is suddenly above the ACSES speed, at some point an overspeed warning will light and it sounds like 5 seconds after that there will be some sort of penalty application if either the brake is in the suppression position or the overspeed no longer no longer exists. Two problems with this system are plainly evident.
First, the braking curve is ridiculously conservative. Every time the ACSES speed began to drop, the engineer was able to get well ahead of the dropping curve without anything close to "aggressive" braking. The capabilities of the equipment have been completely ignored and some leisurely braking rate has been chosen. If PTC "ideal" is to stay out of the engineers way except in case of a dangerous condition, the penalty braking curve should follow the full service braking rate. SEPTA paid both $ and weight for full dynamic, disc and tread brakes on the Silverliner V, which should allow for later braking into curves and stations. Are we now to believe that was just a waste?
Second, the human factors of the speed countdown entourage the engineer to just proceed at slower speeds to avoid potential overspeed warnings. You can watch the student here get dinged by ACSES a couple times, and later, at the instructor's urging, keeps the train at a slower than authorized rate of speed in anticipation of another speed countdown. This is exactly the sort of behavior I warned of and is not exactly what is happening. In addition to a realistic braking curve, the system should try to be invisible and not trigger compensating behaviors. A warning light at 3mph above curve followed by a penalty application at 6mph is all that is needed. This is the standard used on the British Rail ATP system back in the 80's.
An additional item I wanted to quickly point out is the positive stop distance encountered southbound at NEWTOWN JCT (see video, its multiple car-lengths).
UPDATE: The effects of the ACSES roll out were evident in SEPTA's January 2017 schedule. Travel times were uniformly increased on the Media and West Trenton lines between 4 and 6 minutes. Again this runs completely counter to the PTC propaganda that operations would not be affected.
I first want to let everyone know that I now have confirmation that the NS PRR Main Line re-signaling program is not pausing at Lewistown, but has now reached as far west as Huntington. I hope to be able to get out there, but I am as of yet unaware of their timeline. Let's prey for a harsh winter as it would go far in slowing things down.
I can also report massive on Chicago Line re-signaling efforts are pretty much sweeping up everything between South Bend and Chicago including the former BEND interlocking itself, which itself was re-signaled back in the mid 90's to replace the old BEND tower. Multiple new interlockings are in service along with a lot of layout changes (including segments of third track). The former PC-style I-beam gantries at CP-501 and CP-502 have been replaced and older NYC era gantries will soon follow.
However the late model NYC cantilever just east of South Bend did not yet appear to be marked to replacement.
File photo
There is also evidence that some of the PRR PL's on the NS Marion Branch are also going to survive a bit longer.
On CSX some ominous signs are appearing around Akron, the last bastion of CPLs on the old B&O Main Line.
CSX resignaling is now invading the Atlanta area on both their searchlight and elephant ear territory.
While on the former SCL route to Alabama, the re-signaling has reached the GA/AL state line.
For another piece of good news, here is a fine example of the robustness (wind resistance?) of newer style Darth Vader signals that replaced the lower profile MC style searchlights on the former NYC Main Line.
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In hindsight, 2016 was a pretty rotten year with a number of tower closures and major re-signaling projects, but compared to other events and past years, it was kind of tame (and I was able to get out and document more stuff compared to 2015).
So I go on a lot about various signaling systems being "ruined" when reliable relays are replaced by hackable computer based logic or when artisnal hardware is replaced by the equivalent of cheap fast food. Well at some point in the recent past, NJT went out and made its signaling system on the Atlantic City Line just plain worse. After the two recent overspeed derailments on MetroNorth and Amtrak, the FRA made the two railroads install cab signal drops at places where the speed limit decreases be more than 20mph in an attempt to have ATC enforce the civil speed limit. This was part a cudgel to speed the adoption of the ACSES PTC system and part safety theatre since the blunt require didn't take into consideration the actual risk of derailment (in fact MNRR eliminated many of the problem locations by lowering the speed in stages each individually less than 20mph).
Well I don't know how NJT got caught up in this, but I noticed that all green signal lamps had been removed from the northward ABS signals at MP 7 (A72) and MP 8 (A86) south of a 30mph speed restricting through the Haddonfield Trench. The A72 signal is located at the approximate southern limit of the restriction and also serves as the distant to SOUTH RACE interlocking. A 30mph PSR board for the restriction is in place and located about halfway between the two signals.
Modified A86 signal with no High Green lamp.
It appears that NJT has run afoul of the whole craze to "protect" hazardous speed restrictions and normally an 80mph to 30mph drop might seem hazardous, however I should point out that most of the 30mph restriction is not due to track curvature, but complaints from people in town about vibrations from trains in the trench cracking their foundations. While there is a curve at the north end of the restriction, any train passing the A72 signal would be slowed in time by a cab signal drop there and only there. Moreover, at least Amtrak had the common sense to work with its existing setup, jumping relays to force adverse signal indications at adjacent signal locations without any other modifications since, in theory, the changes were temporary. In this case it appears that NJT is settling for reduced speeds, indefinitely.
Modified A72 signal with no High or Bottom Green lamps
Now because the signals are approach lit I couldn't verify what exactly NJT was up to here. Were they giving an Advance Approach on A86 followed by an Approach on A72 to make sure that trains couldn't accidentally go more than 30mph around a curve and through a trench that was likely good for 60mph? Given the removal of the Approach Medium option at A72 that seemed to be the most likely case until I paid a visit to SOUTH RACE and observed this.
The southward signal at SOUTH RACE had also lost its Green lamp and was now displaying Advance Approach as its least restrictive indication. So either an overspeed on southbound trains is less risky than an overspeed on northbound trains going around the same curve, or the A72 signal was also modified to display Advance Approach, despite Approach Medium getting the same 45mph ATC enforcement.
I would have been fine with the A72 being pegged at Approach Medium and the northward signals at SOUTH RACE being pegged at Approach because both alterations are clearly temporary and provide adequate mitigation against a very unlikely situation. What NJT decided to do instead took time, effort and appears to be permanent. This is exactly the sort of problem that PTC is inviting, safety margins being stacked on top of eachother. The overturn speed is 60, but other factors cause the PSR to be set at 30, ACSES will enforce the 30 with conservative braking curves, then cab signal drops will extend the restriction even further (2 miles) away from the curve. Then people wonder why nobody rides public transportation.
Last week, while on a field trip to Chicago, I encountered a new Class 1 railroad signal indication I was hitherto unaware of. Approaching Tower B-12 interlocking on the former Soo/Wisconsin Central line (now owned by Canadian National) to Chicago on a METRA North Central Service train, I saw a signal flashing yellow over a steady green (*Y*/G) This was nothing I had ever encountered before, however it was not difficult to surmise that it was Advance Approach Diverging. At the next interlocking I was proven correct as a Y/G Approach Diverging was displayed for a R/G Diverging Clear at Tower B-12. The Advance Approach Diverging was warranted for the short signal distance between the Approach Diverging at Junction 16 and Tower B-12.
Upon reviewing my CN documentation from 2010, both this and Diverging Clear Approach Diverging (R?*G*) were listed in the operating rulebook, so I should have been aware of it, but I usually refer to the late 90's rule card I have in a more accessible location. I suspect that the signal was likely deployed for the first time for the re-signaling project on the NCS line and might even be a unique situation. It's still an interesting developing for a route signaled line as most others begin to employ speed signaling to various degrees. Of course I should save any more in depth analysis for my BKASS article on CN route signaling ;-)
