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Monday, December 12, 2016

How to Ruin Your Signaling System (For Real)

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).

NJT Comet IB cab car in the Haddonfield Trench
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.

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