Boston to a T explains the limits of automatic vehicle identification on the Green Line.
He doesn't sound at all like Mr T to me.
...will learn it's not pronounced TREE-mont Street.
A few things I don't understand about the supposed limitations of this system:
"The only information automatically communicated back to the Control Center is when a trolley has just passed through one of a handful of junctions ... does not specify the destination of the trolley but merely which direction it is headed (inbound or outbound)"
But the article also says a trolley can automatically identify its route to the switches (for example, if it's a B, C, or D approaching Kenmore outbound). So why can't this information be transmitted to the control center?
Then if they installed some more of the trackside receivers, presto, they'd know where all the trains were.
"For example, at the start of each trip the operator must manually enter the trolley’s destination." -- How is that an avoidable limiatation? Any system will require the driver to do this, including the ones on the other subway lines and buses.
I personally find the announcements repetitive and annoying. Especially for the closely-spaced B line stops, where there's barely time after the previous stop to announce the station name 3 times, plus "doors open on the right", and "the destination of this train is Boston College". The newer Red Line trains say much less per station.
Agreed. It comes down to semantics, and how you choose to define "limitations" of the "current system".
Defined narrowly, the current system only does what it does, and so anything that it does not do is by definition outside of the limitations of the current system.
Defined more loosely, tweaks to cajole better functionality within the same system, that can be made using no or negligible $$ and little programming time, would certainly be within the limitations of the current system.
Defined very loosely, tweaks to create much better functionality, without replacing the current system outright but possibly spending small $$ on software programming and transmitter hardware to work alongside the current system, could certainly be called within the limitations of the current system.
It's pretty easy to arrange, probably just send an email to customer service. The far-left display is the Green Line. You can see what they see. The underground portion is shown in decent detail, and the vehicle numbers are listed above each transponder point as they reach it. The aboveground branches are very simple and only list the vehicle numbers that are currently in transit somewhere on the surface, and those that have reached the terminal.
I'm the author of that article. Allow me to clarify some things by including a few more details.
From what the MBTA explained a few months ago during a tour of their control center, the amount of information they receive from the green line equipment is very slim compared to the highly detailed diagrams they have of the red, orange, and blue lines. The junctions that utilize AVI allow them to see which track a trolley has proceeded on to, however, this does not always help in determining its destination. For example, just past Copley outbound there is a junction at which the E line proceeds southbound while the B, C, and D lines continue westbound. Seeing that a trolley has passed through onto the southbound track does help determine that it's headed towards Heath Street. However, a trolley that continues on westbound can still be headed towards one of three different locations. Basically, seeing which direction a trolley is going can't always narrow down its destination to one concrete possibility.
Furthermore, the MBTA has stated that their current AVI system does not work once trolleys start running street level. Thus, anything past Kenmore or Symphony is completely unknown unless the trolley's location is radioed in. The Control Center's green line schematic also does not show much of the street level portions of each trolley line as it's, for the most part, based completely on the data they can actually receive from the AVI detectors. The MBTA has also said that they do not wish to spend money on retrofitting this system in order to provide real tracking capabilities and that there is simply too little information currently available to release anything worthwhile to the public. Instead, they are looking into something along the lines of AVI control code boxes for each trolley which would be able to communicate back to the Control Center and provide actual real-time information and trolley location.
More details regarding exactly why only certain information is communicated back while other information either is not or can't be may be beyond the scope of my knowledge unfortunately.
As for the trolley operator having to manually input the destination, I understand this may not exactly be an avoidable limitation. Perhaps though, with more advanced technology, the track equipment could recognize that a trolley is at, for example, Riverside and then adjust the trolley's next destination to Government Center automatically as D line trolleys typically run between those stations. Then if a trolley is a Government Center, the system could ask the operator whether the destination should be Riverside or Boston College. Just an idea and one that would need a lot more thought put into it as trolleys on one line can be redirected to another for schedule adjustments and so on, but that was a thought that crossed my mind.
If you (or anyone else) have any more questions or if I made a mistake somewhere, feel free to let me know!
Thanks for the clarification.
Another approach would be to equip the Green Line trains with the same GPS transponders the buses use, and to integrate the Green Line with the NextBus feed. (Muni in San Francisco is integrated into NextBus.) The problem would be in the subway; I don't know how Muni handles its own tunnel.
Thanks. But I still don't understand.
Does the driver punch a code into the trolley at the beginning of the run that (for example) says it's a C, and then this code is picked up at every junction?
Or does the driver have to push a button at every junction that just tells the track switch to move left or right?
If the former is the case, then the trackside reader in theory could tell the Control Center which route the trolley is on.
But I suspect the latter might be the case, based on what I've heard about how drivers can set multiple switches in places like the Lechmere yard.
If they have this on the Red line too, why does it sometimes announce every stop as Davis Square?
I'm not exactly sure, but my guess would be that perhaps the train is reading the tag incorrectly. I've gotten on an inbound red line train at South Station and it was announced that the next stop is Wollaston, but then later it was announced that we were entering Downtown Crossing so maybe it's that.
I've also noticed on the C and D lines that "entering Kenmore..the destination of this train is Government Center/North Station" is never announced when heading inbound. In this case, the tag might either be damaged or missing.