As the opening day of the Long Island Rail Road's decades long East Side Access mega project approached there appeared a new hiccup. Apparently the ESA tunnels were not built to support some of the LIRR's diesel rolling stock that routinely runs to New York Penn Station. Setting aside how the LIRR managed to make their brand new tunnel more restrictive that what it typically the gold standard in limited clearance, someone somewhere noticed that a mis-routing could do a can opened job on an oversize train and demanded that the LIRR perform some mitigation.
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The typical way one would accomplish this would be to have a system of interlocked high car detectors. Tripping a detector would immediately cancel the route and the train would be stopped via both the Cab Signal ATC and ACSES PTC systems. What was so baffling about the LIRR's PTC waiver request was that they were trying to install a new "Tunnel Collision Avoidance" capability to ACSES that would allow for a positive stop at a non-absolute signal or signal indication point. The ACSES positive stop system functions via a transponder telling the on board system to enforce a positive stop in X feet if no cab signal code or radio release is received. This feature was expanded to also cover trains without functioning CSS getting a positive stop at an absolute signal not displaying Rule 280a "Clear to Next Interlocking". TCA would likely work in the same way with a transponder setting up a "positive stop unless" condition combined with a high car detector linked radio release or a cab signal code being present. In fact I think it is actually the latter because part of the aforementioned waiver notes that the ESA tunnels all use only the 250hz cab signal carrier frequency and overheight equipment (DE/.DM30's with C3 coaches) cannot detect the 250hz carrier at all. (See note below)
So my reaction to this is why the heck is the LIRR scrambling to modify ACSES when this was seemingly a solved problem. The fact a waiver is being applied for at all answers part of my question as this must have become an issue only after all of the HAROLD design and signaling work was specified and completed. My Spidey sense tells me that the LIRR's original solution was the use of the 250hz CSS carrier that would drop the cab signals of Amtrak, Metro-North and DE/DM stock to Restricting, at which point the engineer would stop the train short of the low tunnel. Regardless, the Powers That Be demanded a positive stop and instead of adding a new absolute signal at the tunnel mouths, the LIRR decided to do a software fix. I can see how trying to add an HCD system to HAROLD could result in a lot of costly testing given the number of potential routes involved. (After all, the cost of testing prevented NS from even changing the Conrail era HCD recording at CP-BANKS until the general re-signaling project in 2018!), but a couple of extra holdout signals seem pretty straightforward. Based on the general discourse of NYC project management, I suspect the cost of constructing even something "simple" in New York City made a signal-vendor supplied software fix the "better" option.
Before I wrap this up I want to complete the NYC-Region trifecta of poor public sector planning, high cost and political posturing by pointing out the letter that accompanies the FRA's granting of the rather short term PTC waiver. With everything the LIRR is doing to prevent mis-routes including route-indicating signals, rulebook rules, locked out routes, ATC enforced 15mph speeds and the 250hz fail safe cab signal code trick, I would have expected the FRA to issue a letter that states something on the order of "you have gone above and beyond to mitigate this problem". Instead the letter goes on at length about how everything I mentioned is somehow deficient and they reluctantly approve of the waiver. Here's an example.
"The Board also shares Brotherhood of Railway Signalmen’s concerns about LIRR’s existing hazard detection system not protecting Amtrak trains operating in the Harold Interlocking from being misrouted to the GCM tunnel. FRA notes, however, that if an Amtrak train operating with oversized rolling stock is routed towards the GCM tunnel, a series of redundant protections exist to prevent that train from entering the tunnel. First, if a route into the tunnel is incorrectly lined so that an Amtrak train with oversized rolling stock is lined for movement into the tunnel, the train’s PTC system will enforce a positive stop at either signal 11W or 65W. To proceed past either of those stop signals, the train engineer would have to obtain dispatcher permission to by-pass the PTC enforcement and would be held to a PTC enforced 15 miles per hour (mph) speed limit. Second, as a train approaches the signals and diverging switch that controls the tunnel entry track, the train crew will see routing arrows on the mast of the relevant interlocking signals (up to three signals in advance), which will illuminate white when a route is lined from any of the tracks to the GCM tunnel (the arrows will not illuminate if the track is not lined for the tunnel entrance). This will provide Amtrak train crews the opportunity to stop their train, as required by Amtrak’s special instructions. Third, in the event an oversized train passes the 11W or 65W signals because of human error or a failure of the PTC system, and the train crew does not notice the illuminated arrows and take appropriate action if they are operating an oversized train, LIRR’s cab signaling and ATC systems will protect the Amtrak train, as it would any oversized LIRR train, through the 250 Hz cab signal code which will provide an audible alarm and enforce restricted speed."
If you don't want to read all that I can summarize in a 14 second video clip.
What's even more telling is that its the railroad signaling union that is explicitly complaining about the lack of TCA capacity. Just remember, whenever a Union is applying political pressure there is likely overtime to be had. Now, the Railroad Safety Board is a political entity and they are going to do whatever they can to cover their asses to the max and/or avoid political problems with unions that might still provide a few Democratic votes, but the waiver also includes at least 6 safety theatre-esque action items that will add more time and cost to the entire ESA enterprise. Is a mis-route possible? Absolutely, they happen all the time.Even with all the protections could we actually get the can-opener effect? Well an Amtrak Keystone did go to Cynwyd 🤷. Still, the likelihood of all these Swiss cheese holes lining up is remote, especially as there are countless locations along busy passenger tracks where a bad route can take a train into a yard or an out of service track and they aren't causing major safety problems. If rail is every going to deliver nice things, we can't have this level of of CYA virtue signaling coming from the top.
PS: The entire docket of documents related to this waiver, including that super useful HAROLD interlocking diagram, can be found here.
*Note: The PRR legacy Cab Signal System as now deployed in North America makes use of code rates in pulses per minute and one or more AC carrier frequencies in cycles per second (hertz). These can be combined to increase the number of usable codes if so desired. Railroads on Amtrak's Northeast Corridor make use of a 100hz carrier for the basic CSS codes and a 250hz carrier for additional codes that were added ~1999. The LIRR uses an expanded set of pulse code rates and therefore does not need a secondary frequency. This means they could make the EMU stock (M3's, M7's and M9's) sensitive to both a 100hz and 250hz carrier with the same code rates. All other equipment including Amtrak, Metro-North and DE/DM stock will receive a Restricting cab signal in the abstinence of a 100hz code.
