CharlieCard / Ticket discussion

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Yellowspoon
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Re: CharlieCard / Ticket discussion

Post by Yellowspoon » Mon Jun 24, 2019 7:36 am

Where is the value of a Charlie Card (or ticket) stored? Are all fare boxes/gates in direct communication with a central computer al all times?

This may have been discussed before, but 1600 posts are a bit much to wade through.

Once, I checked the value of my Charlie Card (CC) before I boarded a train at Waban. I alighted at Copley. When I entered at Copley for another trip, the fare gate said some gibberish that I don't remember. When I alighted at Brookline Hills, I decided to check the value of my CC. Although I'd boarded twice, only one fare had been deducted. I reboarded an hour later. When I alighted at North Station, all three fares had been deducted when I checked the value.


And as a trivia point, why do I tap my card a 2nd time when I add value? I've always wondered what would happen if I (A) tap my card to add value, (B) put $10 in the machine, and then fail to tap my card a second time.

troffey
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Re: CharlieCard / Ticket discussion

Post by troffey » Mon Jun 24, 2019 3:55 pm

Yellowspoon wrote:
Mon Jun 24, 2019 7:36 am
Where is the value of a Charlie Card (or ticket) stored? Are all fare boxes/gates in direct communication with a central computer al all times?
...
And as a trivia point, why do I tap my card a 2nd time when I add value? I've always wondered what would happen if I (A) tap my card to add value, (B) put $10 in the machine, and then fail to tap my card a second time.
As I understand it, the two issues above are interconnected. If you add value or a pass to your CharlieCard via the T website, it doesn't show until you've tapped it at a fare gate and updated. Additionally, I don't think the RFID in you Card would have the information that you had added value, although I haven't actually tried it. My understanding is that the Charlie machines and gates are in contact with the brains of the system, and your Card only holds the specific information the system tells it to.

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Disney Guy
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Re: CharlieCard / Ticket discussion

Post by Disney Guy » Tue Jun 25, 2019 9:47 am

I am led to believe but am not sure that fare machines, fare gates, and fare boxes are synchronized with a central computer but not sixty times per minute 24 hours a day.

The card also carries the latest usage information as a redundant method of synchronizing with the central computer.

By tapping your card the second time, after making a payment, that synchronizes the card with the fare machine or fare box regarding the latest payment. I take it that for a bus or streetcar the central computer will be updated when the card is tapped at a (stationary) fare gate or (for customer verification) tapped at a fare machine or when the fare box decides to do a bulk update synchronizing for many customer paid fares whichever happens first.
(To the theater stage manager) Quit twiddling the knob and flickering the lights while the audience is entering and being seated. (To the subway motorman) Quit twiddling the knob and dinging the doors while passengers are getting off and others are waiting to board.

MBTA3247
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Re: CharlieCard / Ticket discussion

Post by MBTA3247 » Tue Jun 25, 2019 11:01 pm

The value is stored on the card or ticket itself, along with the last time it was used. The system would collapse otherwise, as the fareboxes on the trolleys and buses are only updated on a nightly basis, and have no other way to determine the value or pass on the card/ticket. This magnifies one of the big problems with the tickets, as stored-value tickets have to be run through the reader several times as it first scans the current value on the ticket and then writes the new value.

When you're adding value to a CharlieCard, the first tap is when the FVM scans the current value on the card; the second tap is when it writes the new value or pass that you just bought to it.
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diburning
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Re: CharlieCard / Ticket discussion

Post by diburning » Wed Jun 26, 2019 12:34 am

Yellowspoon wrote:
Mon Jun 24, 2019 7:36 am
Where is the value of a Charlie Card (or ticket) stored? Are all fare boxes/gates in direct communication with a central computer al all times?

This may have been discussed before, but 1600 posts are a bit much to wade through.

Once, I checked the value of my Charlie Card (CC) before I boarded a train at Waban. I alighted at Copley. When I entered at Copley for another trip, the fare gate said some gibberish that I don't remember. When I alighted at Brookline Hills, I decided to check the value of my CC. Although I'd boarded twice, only one fare had been deducted. I reboarded an hour later. When I alighted at North Station, all three fares had been deducted when I checked the value.


And as a trivia point, why do I tap my card a 2nd time when I add value? I've always wondered what would happen if I (A) tap my card to add value, (B) put $10 in the machine, and then fail to tap my card a second time.
The value is stored on the card, but if you register your card, the MBTA can/will actively track the value on it (so that if you lose it, they can flag the card as invalid and then issue you a new one with the remaining value). A long time ago, a bunch of MIT students figured out how to hack the value on the Charlie card, and the MBTA got an injunction to prevent its release at DEFCON until the vendor, Scheidt and Bachmann, could fix it. Having seen the presentation released after the fix, the value was stored unencrypted, and anyone with knowledge of how hexadecimal worked could alter the values.

As for your trivia point, assuming you are at a fare vending machine, if you insert $10 cash and fail to tap your card a second time, the transaction times out, and it spits out 10 dollar coins into the bottom like a slot machine. If you tapped a different card instead of the card you tapped the first time, it will show you an error, and then spit out the coins. If you're talking about the farebox, the farebox will do one of two things. It could either time out and spit out a flimsy unlaminated paper ticket with your $10 on it, or it could just take the $10 and give you nothing. (in which case, you'd have to contact the MBTA about your loss, and they'll hand count that farebox when they get around to emptying it, to see if there's an overage).

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Disney Guy
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Re: CharlieCard / Ticket discussion

Post by Disney Guy » Sun Jun 30, 2019 9:09 am

When a rider inserts too much into a fare box for a cash fare, the flimsy card that comes out representing the change has a mag stripe on the back and can be used as a Charlie Ticket, although in most cases "add fare" has to be done at a fare vending machine before the next usage.

I think that the same kind of card would come out if a rider inserted cash into a fare box and failed to tap a Charlie Card a second time there.
(To the theater stage manager) Quit twiddling the knob and flickering the lights while the audience is entering and being seated. (To the subway motorman) Quit twiddling the knob and dinging the doors while passengers are getting off and others are waiting to board.

RenegadeMonster
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Re: CharlieCard / Ticket discussion

Post by RenegadeMonster » Sun Jun 30, 2019 5:51 pm

Hmm, Maybe, but in my experience about 3 years ago I got a pile of dollar coins.

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