Preamble
This is the article text as it appears in the Spring 2005 issue of 2600 Magazine. Also available as a PDF.
In order to clear up some confusion, my pen name for this and the Magnetic Stripe Reading article was Redbird. I am the author of these articles and no, they're not being published without citation. I hereby give credit to the author: myself.
Introduction
In this article, I will explain many of the inner workings of the New York City Transit Authority fare collection system and expose the content of MetroCards. I will start off with a description of the various devices of the fare collection system, proceeding into the details of how to decode the MetroCard's magnetic stripe. This article is the result of many hours of experimentation, plenty of cash spent on MetroCards (you're welcome, MTA), and lots of help from several people. I'd like to thank everyone at 2600, Off The Hook, and all those who have mailed in cards and various other information.
Becoming familiar with how magnetic stripe technology works will help you understand much of what is discussed in the sections describing how to decode MetroCards. More information on this, including additional recommended reading, can be found in "Magnetic Stripe Reading," also in this issue.
Terms
These terms will be used throughout the article:
- FSK - Frequency Shift Keying
- A type of frequency modulation in which the signal's frequency is shifted between two discrete values.
- MVM - MetroCard Vending Machine
- MVMs can be found in every subway station. They are the large vending machines which accept cash in addition to credit and debit.
- MEM - MetroCard Express Machine
- MEMs are vending machines that accept only credit and debit. They are often located beside a batch of MVMs.
- MTA - Metropolitan Transportation Authority
- A public benefit corporation of the State of New York responsible for implementing a unified mass transportation policy for NYC and counties within the "Transportation District".
- NYCTA - New York City Transit Authority
- Under the control of the MTA, the NYCTA is a public benefit corporation responsible for operating buses and subway trains in NYC.
- RFM - Reduced-Fare MetroCard
- RFMs are available to the elderly or people with qualifying disabilities. Typical RFM fare is half or less than half of the standard fare.
- "Common MetroCard"
- This term will refer to any MetroCard available to the public without special requirements. Examples include standard pay-per-ride cards, standard unlimited cards, and single-ride cards.
- "Special MetroCard"
- This term will refer to any MetroCard not available to the general public. Examples include reduced-fare cards, student cards, and employee cards.
- "Single-Track MetroCard"
- This term will refer to any MetroCard that has a one-track magnetic stripe (although there is no visible difference between the stripes of these cards and the stripes of two-track cards). The following types of cards are single-track: Single-Ride and Bus Transfer MetroCards.
- "Dual-Track MetroCard"
- This term will refer to all MetroCards with the exception of the single-track MetroCards mentioned above. The following types of cards are some examples of dual-track cards: pay-per-ride, pre-valued, unlimited, and reduced-fare.
- "Passback period"
- This term will refer to the time period before an access device will allow you to use an unlimited card again after swiping it. During this period, the devices generally respond with the message "JUST USED".
- "Standard cards" and "standard readers"
- These terms will refer to cards containing a magnetic stripe (credit, banking, etc) or readers of these cards that conform to the standards set forth in any or all of the following ISO specifications: 7810, 7811, 7813, and 4909.
Cubic Transportation Systems
The fare collection system the MTA uses is developed by Cubic Transportation Systems, a subsidiary of Cubic Corporation. The patents I found to be related to the current New York City system filed by Cubic Corporation are as follows:
- 4,877,179 - FAREBOX SECURITY DEVICE
- 5,056,261 - TURNSTILE SYSTEM
- 5,072,543 - TURNSTILE MECHANISM
- 5,191,195 - FARE CARD READ-WRITER WHICH OVERWRITES OLDEST OR INVALID DATA
- 5,215,383 - TICKET STOCK AND TICKET DISPENSER
- 5,298,726 - FARE CARD READ-WRITER WHICH OVERWRITES OLDEST OR INVALID DATA
- 5,333,410 - CONTROLLABLE BARRIER SYSTEM FOR PREVENTING UNPAID ADMISSION TO A FEE-PAID AREA
- 5,574,441 - MASS TRANSIT INDUCTIVE DATA COMMUNICATION SYSTEM
- 5,612,684 - MASS TRANSIT INDUCTIVE DATA COMMUNICATION SYSTEM
- 6,595,416 - SYSTEM FOR RAPIDLY DISPENSING AND ADDING VALUE TO FARE CARDS
- 6,655,587 - CUSTOMER ADMINISTERED AUTOLOAD
- 6,789,736 - DISTRIBUTED ARCHITECTURE FOR MAGNETIC FARE CARD PROCESSING
Servicing, apart from routine collection of fares, on MTA equipment seems to be done by Cubic employees, not the MTA.
The MetroCard System
At the core of the MTA fare collection system is the MetroCard. Preceded by a token-based system, the MetroCard is now used for every aspect of fare collection and allows for fare options that would never have been previously possible (e.g., Employee, Reduced-Fare, and Student MetroCards). MetroCards can currently be purchased at MVMs, MEMs, token booths, and various merchants throughout the New York City area. I will categorize the MetroCard access devices into two types: reading devices and fare collection devices. Both of these devices are networked in a complex system which allows the MTA, within minutes, to have up-to-date information on every card that has been issued. This also allows them to disable any card at will. The hierarchy of the network is shown below (as described in patent 6,789,736).
The physical characteristics of MetroCards follow those of standard cards (see Terms) almost exactly, but are one third the thickness. They have a diagonal notch cut out in the upper-right hand corner 3 1/8" from the left and 5/16" from the top of the card. Additionally, they have a 1/8" diameter hole, with its center 1/4" from the left and 5/16" from the top of the card, which is used to aid machines that suck your card in (bus fare boxes, MEMs/MVMs, handicapped entry/exit machines, etc.).
Vending Machines
MEMs and MVMs are located throughout the subway system. They allow you to purchase or refill various common MetroCards with either cash or a credit card. RFMs can't be purchased at machines but can be refilled. On the front of the MEM or MVM is a tag with the machine's unique ID number.
The BIOS System Configuration screen from an MEM looks like this:
AMIBIOS System Configuration (C) 1985-1997, American Megatrends Inc.,
Main Processor : Celeron(tm) Base Memory Size : 640KB
Math Processor : Built-In Ext. Memory Size : 14336KB
Floppy Drive A: : None Display Type : VGA/EGA
Floppy Drive B: : None Serial Port(s) : 3F8,2F8
AMIBIOS Date : 07/15/95 Parallel Port(s) : 378
Processor Clock : 300A MHz External Cache : 128KB,Enabled
ATA(PI) Device(s) Type Size LBA 32Bit Block PIO
Mode Mode Mode Mode
Primary Master : Hard Disk 5729MB LBA On 16Sec 4
PCI Devices: PCI Onboard USB Controller, IRQ11
PCI Onboard Bridge Device PCI Onboard Ethernet, IRQ15
PCI Onboard IDE
PCI Onboard VGA
FPGA ver. C, Base Address: 500h
BSP CPU.....Microcode OK
I have no reason to believe that the MVM hardware is any different.
Receipts
Receipts can be obtained from MEM and MVM machines by answering "yes" when prompted. They possess a lot of information about the MEM/MVM, subway station, and card. You can match a receipt to a card by comparing the serial numbers. Let's take a look at some samples:
MVM RECEIPT MVM RECEIPT MEM RECEIPT
MTA NYC TRANSIT MTA NYC TRANSIT MTA NYC TRANSIT
ASTOR PLACE NASSAU AV & MANHATTAN AV 14TH STREET & 6TH AVENUE
NEW YORK CITY NY NEW YORK CITY NY NEW YORK CITY NY
MVM #: 0545(R219 0701) MVM #: 1738(N408A 0500) MEM #: 5383(N513 0400)
Sun 14 Nov 04 21:28 Mon 04 Oct 04 14:22 Wed 17 Nov 04 12:14
Trans: Sale OK Trans: Sale OK Trans: Add Time OK
Payment Mode: Cash Payment Mode: Credit Amount: $ 10.50
Amount: $ 7.00 Amount: $ 21.00 Initial Type:030
Card Value: $ 0.00 Card Value: $ 0.00 7-DAY RFM UNLIMITED
Change Due: $ 3.00 Time Added: 030
Credit Card #: XX5346 7-DAY RFM UNLIMITED
Serial #:1059909877 Auth#: 000008
Type: 023 Ref #: 060615762129 ATM Card #: XX0952
1-DAY UNLIMITED Auth#: 760346
Serial #:1027066848 Ref #: 029089559668
Questions? Type: 024
Call (212) METROCARD 7-DAY UNLIMITED Serial #:0987218036
Questions? Questions?
Call (212) METROCARD Call (212) METROCARD
Most of the information on the receipt is fairly obvious, but notice the line that begins with "MEM #" or "MVM #". The first four digits correspond to the actual MEM or MVM ID number as found on the machine. The next letter and following three digits inside the parenthesis correspond to the closest token booth. This ID can also be found on the booth itself. The meaning of the next four digits is currently unknown. However, they are unique to each machine that has the same booth ID, but are not unique among machines with different booth IDs. They seem to simply be a unique ID for each MEM/MVM in the station, possibly grouped by location. See "MEM/MVMs" for a table.
Now look to the bottom of the receipt. The line that begins with "Type:" (or "Initial Type:" if an RFM is being refilled) gives the numerical card subtype value followed by a description of the type on the following line.
Receipts purchased with a credit card contain additional fields that allow the MTA to verify the credit card holder in the case that he/she decides to lose the MetroCard.
Turnstiles
The use of a turnstile is the most common way to enter the subway. Entry is granted by swiping a valid MetroCard through the reader/writer located on the outside of each turnstile. Once swiped, the LCD display on the turnstile will display a message. Some common messages:
- GO
- Message displayed for unlimited MetroCards
- GO
1 RIDE LEFT
- Message displayed for Student MetroCards, where '1' is the number of rides left for the day.
- JUST USED
- The passback period for the unlimited MetroCard is not up
- GO
1 XFER OK
- Message displayed when transferring from a bus.
Above the LCD there are a series of round indicators. Of these, one has an arrow pointing in the direction of the turnstile in which you would enter after paying your fare, and another reads "No" and a do-not-enter bar which, when lit, indicates that the turnstile is not active. After paying your fare, another indicator below the green arrow lights to indicate that you may proceed through the turnstile without smashing your groin into the arm.
Above those, there are three horizontal bar indicators contained within a rectangular cutout. When a Reduced-Fare MetroCard is swiped, the top indicator (red) will light. When a Student MetroCard is swiped, the middle indicator (yellow) will light. When an Employee MetroCard is swiped, the bottom indicator (the color of which I'm unsure of) will light. These indicators are present on both sides of the turnstiles and they allow transit cops, many of whom are undercover, to monitor the types of cards being used by riders. This helps detect, for example, when Student MetroCards are being used at times when school is not in session or when an obvious misuse of an Employee or Reduced-Fare MetroCard occurs.
Reading MetroCards
MetroCards are relatively difficult to read. You will not be able to read them with off-the-shelf magnetic stripe readers, so please don't waste your money. The reason for this is not that the format is different; MetroCards use Aiken Biphase (also known as frequency shift keying (FSK)) just like standard cards. However, the hardware that ships with these readers is designed for a completely different (and well-documented) specification. They require many "clocking bits," which consist of a string of zero-bits at the beginning of the stripe to aid in setting a reference frequency for decoding. Additionally, most readers also look for a standard start and end sentinel that exists on standard cards to denote the start of a particular track. On top of that, characters on these cards are defined as either four or six bit blocks (depending on the track) and contain a longitudinal redundancy check (LRC) character after the end sentinel to verify data integrity. Needless to say, MetroCards don't have any of these properties and contain fields of arbitrary length; thus, another method of reading and decoding is required.
Fortunately, magnetic heads are everywhere (e.g., cassette tape players) and the output from magnetic heads when passed over a magnetic stripe consists of voltage spikes in the audible frequency range. Since sound cards are excellent A/D converters for this range of input and are readily available and very cheap, we can use the microphone input interfaced to a magnetic head for the purpose of creating our own reader (for a lot less than the MTA is paying, I'm sure!). See the article "Magnetic Stripe Reading" in this issue for more details.
For the same reason that reading was initially difficult, writing to MetroCards is extremely difficult, and is still a work-in-progress which will not be discussed in this article. A technique similar to that of the decoder (in reverse) can be used to write to cards, although it is much more difficult to implement and obviously requires more equipment than just a sound card and a magnetic head. For those of you who realize how this can be done and have the ability to build the equipment, kudos, but keep in mind the ramifications of being caught using a card you wrote to yourself. Modifying the data on cards does work. But the MetroCard system is very complex and allows for the surveillance of this sort of activity. The goal of this project is to learn how the system works, how it can be theoretically defeated, but certainly not to get stuck in prison.
Apart from these difficulties, MetroCard tracks are defined as follows: Dual-Track MetroCards have two tracks - one track being twice the width of the other - and will be referred to as track 1-2 and track 3; Paper MetroCards have one track which will be referred to as track 1-2. These track names (as I refer to them) correspond to the same track fields that have been established by ISO 7811.
Decoding Dual-Track MetroCards - Track 3
Track 3 on dual-track MetroCards contains static data. It is written when the card is produced and the serial number is printed on the back, and is not written to thereafter by any machine. Some data found on this track can also be found by looking at the information printed on the back of the card. The track format is as follows:
Track 3 Content Offset Length
--------------- ------ ------
1: Start Sentinel 0 15
2: Card Type 15 4
3: Unknown 19 4
4: Expiration Date 23 12
5: Unknown 35 4
6: Constant 39 8
7: Unknown 47 8
8: Serial Number 55 80
9: Unused 135 16
10: Unknown 151 16
11: End Sentinel 167 93
Decoding track 3 is accomplished as follows:
- Constant: 000000011000111
- Convert binary to decimal
- See "Card Types" for a lookup table.
- Use is not yet known
- To determine the expiration date for common MetroCards:
- Convert binary to decimal
- Divide the decimal value by 2, round up
- Convert the decimal value to year / month format as follows:
- Year: Integer value of the decimal value divided by 12
- Month: Value of the modulus of the decimal value and 12
- Add 1992 to the year
- The expiration date is the last day of the previous month
- Note: Non-common MetroCards seem to have different date offsets (FIXME: find offsets)
- Note: This expiration date is the date the physical card can no longer be used and is considered invalid. See the track 1-2 expiration date field for more information.
- Use is not yet known
- Constant: 00001101
- Use is not yet known
- Convert binary to decimal
- Unused field
- Use is not yet known
- Constant:
00100101001100100110100101100101010011001010010
1001100110101010011010010101001101001010110101
Decoding Dual-Track MetroCards - Track 1-2
Track 1-2 on dual-track MetroCards contains variable data. It is written to by every machine used for fare collection, reading devices excluded. Interestingly enough, track 1-2 does not only contain information pertaining to the last use, but also to the use before that. These two records are separated by a strange set of field separating bits, which contains in it a bit that seems to be half of the one-bit frequency (which is a non-standard use of FSK). The most reliable way to find the second track is to search for a second start sentinel, both of which are identical for each record. The track format is as follows:
Content Offset Length
-------------------- ------ ------
1: Start Sentinel 0 10
2: Time 10 2
3: Card Sub-Type 12 6
4: Time 18 6
5: Date 24 10
6: Times Used 34 6
7: Expiration Date 40 10
8: Transfer Bit 50 1
9: Last Used ID 51 15
10: Card Value 66 16
11: Purchase ID 82 16
12: Unknown 98 20
Decoding track 1-2 is accomplished as follows:
- Constant: 0011010111
- See 4
- Convert binary to decimal
- The card sub-type corresponds to the sub-type as indicated on the receipt if one was obtained from an MEM/MVM.
- See "Card Types" for a lookup table.
- To deal with the limited storage space on the MetroCard stripe, each bit in this field and field (2) represents 6 minutes. To determine the last time used for common MetroCards:
- Concatenate the binary from (2) with the binary from this field
- Convert to decimal
- Multiply decimal value by 6
- Result is the number of minutes since 01:00 that the card was last used
- Convert binary to decimal
- This field contains the last usage date, which can be determined by calculating an offset based on a card of the same type with a last usage on a known date. However, since this field only has 10 bits, dates will most likely roll over after 1024 (2^10) days and a new offset will have to be determined. Offsets also seem to differ with different types of MetroCards.
- Convert binary to decimal
- The times used field is incremented every time you use the card to pay a fare except during a transfer. In that case, the transfer bit is set and the times used field remains the same.
- Convert binary to decimal
- Determine offset based on the description in 5a to determine the exact expiration date of a card. Alternatively, subtract the date field from this field to determine how many days after the last usage the card expires.
- Do not confuse this field with the expiration date field on track 3; it is only used on cards which expire a set number of days after you first use them (eg. unlimited cards) and will not be set for cards such as pay-per-ride which do not have an expiration date.
- Bit is 1 if the last use was for a transfer, 0 otherwise
- Convert binary to decimal
- This field seems to have a completely separate lookup table that is used internally by the fare collection system.
- See "Last Used IDs" for a lookup table.
- Convert binary to decimal
- The result is the value remaining on the card in cents.
- Convert binary to decimal
- This field seems to have a completely separate lookup table that is used internally by the fare collection system to match the value of this field with a MVM ID number (such as those you can find on receipts).
Card Types
Type Subtype Description
0 0 FULL FARE
0 10 PRE-VALUED
0 12 PRE-VALUED ($10.00)
0 13 PRE-VALUED ($2.00)
0 14 LIRR
0 19 PRE-VALUED ($4.00)
0 23 1-DAY UNLIMITED ($2.00 fare)
0 24 7-DAY UNLIMITED ($2.00 fare)
0 25 7-day Express Bus Unlimited ($4.00 fare)
0 26 30-DAY UNLIMITED ($2.00 fare)
0 29 AIRTRAIN
0 30 7-DAY RFM UNLIMITED ($2.00 fare)
0 43 TransitChek
0 46 TransitChek
0 47 TransitChek
0 48 TransitChek 30-DAY UNLIMITED
0 56 1-DAY UNLIMITED ($1.50 fare)
0 57 7-DAY UNLIMITED ($1.50 fare)
0 59 30-DAY UNLIMITED ($1.50 fare)
0 62 SingleRide ($1.50 fare)
0 87 SingleRide ($2.00 fare)
4 2 Two-Trip Special Program Pass
4 5 Grades 7-12
4 13 1/2 Fare - Grades K-12
Last Used IDs
1513 14th St/Union Sq
1519 8th St/Broadway (A39)
1880 Lexington Ave (N601)
1942 ASTOR PLACE (R219)
2157 34th St/6th Ave (N506)
2204 42nd St/Grand Central
2278 9th Street PATH
MEM/MVMs
Location Type ID
14TH ST. - UNION SQUARE MVM 0530(A033 0400)
14TH ST. - UNION SQUARE MVM 0400(A033 0700)
14TH ST. - UNION SQUARE MVM 0481(A033 0701)
14TH ST. - UNION SQUARE MVM 1122(A034 0400)
14TH ST. - UNION SQUARE MVM 0216(A034 0700)
14TH ST. - UNION SQUARE MVM 0215(A034 0701)
14TH ST. - UNION SQUARE MVM 1370(A035 0700)
14TH ST. - UNION SQUARE MVM 0541(A037 0700)
14TH ST. - UNION SQUARE MVM 0265(A037 0701)
8TH STREET & BROADWAY MEM 5462(A039 0400)
8TH STREET & BROADWAY MEM 5662(A038 0401)
95TH ST & FT. HAMILTON MVM 0982(C028 0700)
14TH STREET & 8TH AVE MEM 5314(H001 0702)
1ST AVE & 14TH STREET MVM 1358(H007 0700)
1ST AVE & 14TH STREET MVM 1145(H007 0701)
175 ST/FT. WASHINGTON AV MVM 1632(N010 0400)
175 ST/FT. WASHINGTON AV MVM 1611(N010 0700)
175 ST/FT. WASHINGTON AV MEM 5274(N010 0701)
W 4TH ST - WASHINGTON SQ MVM 0321(N080 0700)
W 4TH ST - WASHINGTON SQ MVM 0109(N080 0701)
FORDHAM ROAD MVM 0550(N218 0700)
LEXINGTON AVE - 3RD AVE MVM 0740(N305 0401)
NASSAU AV & MANHATTAN AV MVM 1738(N408A 0500)
34TH STREET/SIXTH AVENUE MVM 1428(N506 0702)
34TH STREET/SIXTH AVENUE MVM 0540(N507 0701)
14TH STREET & 6TH AVENUE MEM 5383(N513 0400)
CHRISTOPHER STREET MVM 0637(R125 0700)
CHRISTOPHER STREET MVM 0063(R125 0701)
14TH STREET - 7TH AVENUE MVM 0294(R127 0400)
14TH STREET - 7TH AVENUE MVM 1643(R127 0401)
14TH STREET - 7TH AVENUE MVM 0357(R127 0700)
14TH STREET - 7TH AVENUE MVM 0376(R127 0701)
34TH STREET-PENN STATION MVM 0553(R138 0701)
WALL STREET & BROADWAY MVM 1123(R203 0400)
WALL STREET & BROADWAY MVM 1038(R203 0700)
ASTOR PLACE MVM 0654(R219 0400)
ASTOR PLACE MVM 0586(R219 0700)
ASTOR PLACE MVM 0545(R219 0701)
ASTOR PLACE MVM 0744(R220 0700)
ASTOR PLACE MVM 0318(R220 0701)
14TH ST. - UNION SQUARE MVM 0576(R221 0400)
14TH ST. - UNION SQUARE MVM 0514(R221 0401)
14TH ST. - UNION SQUARE MVM 0475(R221 0700)
14TH ST. - UNION SQUARE MVM 0564(R221 0701)
23RD STREET - PARK AVE MVM 0489(R227 0701)
28TH STREET - PARK AVE MVM 1228(R229 0700)
Conclusion
As you may have noticed, I haven't provided a way to decode the Single-Track MetroCards yet. Bus Transfer MetroCards are collected after use and the magnetic stripe of Single-Ride MetroCards is written with bogus data after use. We simply haven't received enough unused samples to be able to reverse-engineer all the information contained on these cards.
This project is far from over, and we still have tons of data that needs to be collected. You can help in many ways:
- Collect receipts every time you purchase a MetroCard. This will help us expand (and keep updated) our database of the booths and MEMs/MVMs contained within each station. Also, if possible, keep the MetroCard associated with the receipt.
- If you notice anything unusual, such as a frozen MTA kiosk (eg. MEM, MVM, reader, etc), open equipment (eg. while repairs are being done), or anything else, take some good pictures. As of now, photography bans are being proposed for New York City subway system, but are not yet in place. It is not yet illegal to take pictures, so know your rights.
- If you're paying for a bus ride with change, get a Bus Transfer MetroCard and send it to us if you don't intend to use it. Make sure you note the route, direction, time, date, and any other applicable information.
New things are being discovered and more data is being collected every day, so consider this article a "snapshot" of a work in progress. You can find and contribute to the data being collected on this system at http://www.2600.com/mta and by sending us additional information at 2600 Metrocard Project, PO Box 752, Middle Island, NY 11953 USA.
Addendum A (2006-07-28)
Due to numerous requests, included here is a (sloppy) Perl script which can be used to parse raw binary MetroCard data, such as one from dab. Simply pipe the output of dab into the following script:
dmc.pl (v0.1)- Decode MetroCard Magnteic Stripe Binary
types.txt - Sample types.txt file
lids.txt - Sample lids.txt file
After my presentation at HOPE Number Six, many people expressed great interest in the project. As it stands now, nearly a year has passed since I've done any extensive research on the system. However, most aspects of how the NYCTA's fare control works can be relatively well understood with what has already been done. I think the whole project stands as a good example of how the process of reverse engineering works and a model for those interested in dissecting systems of their own interest.
Although I'm always looking to learn more, digging deeper into this specific project has the potential to open a relatively large can of worms, namely exposing enough information to facilitate the creation of illegitimate cards. This, of course, is not my intention. I've explained the exploits that have existed in the past and how they'd worked only because public knowledge of them was already available (but without a technical explanation). Only after the MTA implemented safeguards against them did I explain how the exact exploit was carried out. But a stored value system such as this is inherently flawed and there are more vulnerabilities present. My goal was always to show how these systems work (as well as their flaws) because I believe that such knowledge should be made openly available, as it can only help increase the security of future systems. So if anyone else has any interest in continuing the research, you're more than welcome to, and I'll update this page accordingly. But for now, I think it's time for me to move on. I appreciate all of the encouragement and support that many of you have offered. Oh, and the zillions of MetroCards too! ;-)
Currently, rumors are that the MTA has plans to deploy an RFID system to replace the MetroCard. A trial run with MasterCard PayPass technology is being conducted on the 4,5,6 line. If these tests are successful (and I have no reason to believe that they wouldn't be), the likelihood of a system-wide RFID deployment seems very high. I'm looking forward to exploring the next generation of transit fare cards in New York City with all of you again in the near future. Thanks for all of your interest!
Regards,
~Redbird
P.S. The 2600 MTA Wiki page is no longer being maintained (unfortunately, it never really caught on). Also, a more convenient address to send 'stuff' to is P.O. Box 29, Fort Lee, NJ 07024-0029 USA.
Addendum B (2006-08-05)
Thanks to Fred Hopper, who was kind enough to give me a bottle of magnetic developer fluid (expensive stuff!), I can now show exactly how the tracks are physically laid out on the card. This may help explain my "track 1-2" terminology! ;-)
Another interesting tidbit here is that you can see how writes from different turnstiles are aligned. Look closely at track 1-2 of the top card -- so many MetroCards are swiped each day that they actually wear down the steel base of the turnstile readers and the magnetic heads start reading and writing above where they should. It's becoming enough of a problem now that they've developed inserts that raise the card resting level on badly worn readers.
