The T posted about the
Green Line Train Protection System on Instagram a few days ago. It's the first time I'm hearing about it - anyone know if it's block signaling like the other lines have, or something more like CBTC? I wouldn't even dare to dream of it being something like automation for the downtown segments...
FCMB had a presentation on this in May giving more detail on the concept:
https://cdn.mbta.com/sites/default/...int-26-green-line-train-protection-system.pdf
It's not a full-on replacement signal system like Red/Orange ATO cab signals or CBTC with moving blocks, but an overlay to the existing block signals serving similar additive function as RR Positive Train Control. It uses radio transponders to advance-warn about the upcoming block and apply controlled braking. Therefore the block layout does not change (except for the parts GLT is already streamlining, like eliminating the timered auto-stops), but operator adherence is guaranteed for both the speed limit and enforced stops. In addition to all the prevention provided, it will allow return of 50 MPH speed limits on the outer D Line because safe max-speed operation won't be compromised by variable (esp. in certain sun glare situations) visibility of the wayside signals.
The other--separate--piece is a collision avoidance camera/sensor array on the trolley that monitors train-to-train spacing and enforces braking therein. This is the prevention for rear-end collisions that the block signals & PTC cannot (without traffic-punitive layout changes) 100.00% prevent, and solves for the Central Subway's dilemma of supporting incredibly close train spacing...where earlier studies of full-on CBTC uncovered problems maintaining current TPH levels. This has the added benefit of track-level obstruction detection like slamming the brakes before a dumbshit driver runs a red trying unsuccessfully to beat the trolley across a reservation grade crossing, or the annual BU move-in week rite of scraping some freshman off the grill of a B train. This is probably also the solution for making Mattapan fail-safe sans signal system. They don't have to worry about block adherence out there because TPH and spacing are simply too low to merit a wayside install...but the HSL definitely needs the line-of-sight assist for collision avoidance and whacking a couple sightline-induced speed restrictions (like the cemetery curve which is more arbitrarily severe in one direction vs. the other because of lesser sightlines).
The back-end improvements all involve continuing the wholesale replacement of any remaining copper signal relays to all-fiber, and renewing all remaining signal heads to low-wattage, hermetically sealed LED's. The fiber backplane
would allow them in the future to open-heart transplant the signal system to full-on CBTC if subsequent design efforts produced a winner that would work for the Central Subway's traffic levels. In much the same way that RLT/OLT passed up CBTC on this go-around to (1) optimize the shit out of its incumbent ATO in the interim, and (2) cleanroom full fiber backplanes line-wide...but gain the plug-compatibility for a way easier/smaller-step upgrade to moving-block CBTC in some later decade by going to the well now with fiber and a back-port of the existing system. Fiber's high bandwidth would allow them to co-install some sort of newfangled moving-block CBTC system optimized for a mixed-environment LRT system, test it independently off the same fiber plug-in while the old wayside + PTC system is still active, then do the migration on their own pace. Sets up a much easier two-step upgrade path towards the ultimate goal. It's a big learned lesson from NYC's utterly tortured signal renewal where they're rockheadedly installing all-new AND maintaining the century-old copper relay systems in tandem for a way slower, more expensive, more labor-intensive rollout. The T is drawing the correct learned lesson from NYC's disaster of biting off so much more than it could chew by prioritizing the high-bandwidth backplane needs to come first BEFORE necessarily changing the core signal system. Because if you're ultimately going to go full- Jetsons Shit with the signal system you better well have all the prereqs in place in full working order first AND have the spare bandwidth on all that cable plant to juggle old + new signal systems off one set of computers during such a major, major technological transition. Therefore, much like CBTC may be an eventual 2030+
lower-key (thanks to the ongoing prelim work) addition to Red/Orange's repertoire for sake of installing 'self-healing' moving blocks that help preserve the long-term sanctity of the 3-min. headway that the current ATO signal optimization first-time enables...you may see a future jumping-off point with Green if the service layout (say...plugging in those all-critical future Seaport-Downtown and/or Urban Ring patterns) substantially changes requiring something a bit more overall-dynamic than this current hybrided signal upgrade. The new backplane will support similar future upgrade paths, and the two-step upgrade plan similarly incoculates them from stubbing their toes on unforeseen problems with an all-or-nothing upgrade like NYCTA has.
www.bostonglobe.com
