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Wednesday, December 4, 2013

Non-Conditional Cab Signal Drops

In the wake of the recent Metro-North derailment I wanted to share a few bits and pieces on non-conditional cab signal drops as a way to control train speed for non-signaling related reasons or to warn Engineers in advance of a particular hazard. While Cab Signaling or any kind of signaling is typically seen as a way to warn trains of dynamic hazards, there have always been cases where signaling has been employed as a tool to show trains for static hazards. Typically railroads have preferred to use line speeds for such static hazards as the regulatory issues and costs are much less. Case in point being equilateral turnouts where all routes get Clear signals and the restriction is listed in the employee timetable. However on speed signaled roads the most common use of signaling to control timetable speeds is seen with slow speed terminal trackage where all routes, straight and diverging, are signaled for 15 mph.

If one scours enough interlocking diagrams it is easy to find examples where what might meet the signaling definition of a "straight" or Normal Speed route provides a more restrictive signal indication in order to deal with a particular high risk speed restriction. One well known example was the former CP-WEST PITT interlocking on the Conrail Pittsburgh Line that retained its 15mph Slow Speed routes due to a sharp curve west of the Pittsburgh Station. Even after the interlocking was removed westbound trains still encounter an Approach Slow at CP-PITT or CP-EAST PITT before the MP353 automatic displaying Clear.

Signaled speed restrictions are certainly more expensive or signs or ink.
 Technical signaling enhancements like IIATS and the British AWS both contained mechanisms for non-conditional activation, which had the benefit of being cheap to employ due to there being no need for attached power or logic in such situations. To this day there are a number of ATS protected speed restrictions on the former ATSF "Super Chief" route from Chicago to Los Angeles, even outside of ATS territory as locomotives on the route are generally ATS equipped.

1920's technology is sufficient to alert a drowsy Engineer.
 This finally brings up the use of "phantom signals" or non-conditional cab signal drops to control train speed at high risk speed restrictions. I have heard this was employed in a number of locations by the PRR, but was unable to find any references for that, but the most notable use of this practice came from Amtrak in the result of the Back Bay Derailment in the late 1980's where a high speed Amtrak train approaching Boston at 100mph failed to brake in time for the sharp 30mph curve at the west end of the Back Bay station. As a result Amtrak agreed to install non-conditional cab signal drops at a number of "high risk" speed restrictions along the Northeast Corridor. These include:

* BAY Interlocking near Baltimore for southbound trains.
* Frankford Junction Curve outside Philadelphia for southbound trains.
* Elizabeth, NJ S-Curve for northbound trains.
* Boston Back Bay station for northbound trains.

Unlike a rapid transit system with some sort of hard ATC or ATO system where the speed is enforced through the entire restriction, Amtrak's method dropped a Clear (125mph) cab signal to an Approach Medium (45mph) signal and then lifted it after a distance sufficient for the Engineer to apply a brake application sufficient to suppress the Automatic Train Control system.

While other eastern commuter railroads such as SEPTA and NJT have installed similar "speed control" cab signal drops on their territories, Amtrak's did the best at getting the train to slow without sufficiently gumming up the works. For example SEPTA now has extensive cab signal speed enforcement in the area of JENKIN interlocking that goes beyond what is required by timetable speeds and NJT recently re-signaled the approach to the Delair Bridge with a non-conditional Approach Limited at the new JORDAN interlocking replacing what had been Clear signals all the way across the bridge and hitting trains with a 2-mile 45mph slow zone.

Anyway the real reason I brought this up was because I actually found a sweet video on YouTube showing a Metroliner cab car as it runs at the front of a Keystone train from Linden, NJ through the Elizabeth S-Curve. You can watch the cab signal drop about 50 seconds into the video and then pop back up about 30 seconds later before the train even gets within sight of the curve. Still, the speed has been slowed and the Engineer still has sufficient operational leeway to not lose time.



There is no reason that Metro North should not have adopted this practice sometime in the last 20 years for the clearly high risk speed restriction at Spuyten Duyvil. The northern limits of CP-12 are 0.7 miles from the curve and the southern limits 0.2 miles. A non-conditional cab signal between those two points would have provided ample warning to any drowsy engineer with room to bring the train to a complete stop if necessary.  I am sure MNRR will apply this "solution" both at the Spuyten Duyvil curve (and, I assume, the similar curve at New Rochelle) in advance of whenever they complete their PTC project, but keep in mind that the PTC project that will cost 300-500 million dollars on Metro-North alone would have been just as effective as the existing ATC technology if used properly. Why pay more?


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