Magnetic-stripe, read-only

Magnetic-stripe readers are devices that read and decode the information contained on magnetic-stripe tickets. Please see the section magnetic-stripe tickets for information on the tickets themselves, and how they are used in the passenger transport sector for fare collection.

The core element of a magnetic-stripe reader is the reading head, which generates an electrical field. As the stripe passes over it, the reading head detects the variances in the magnetic field along the stripe. It decodes these variances into binary bits, which are transferred to the reader’s microprocessor for analysis and performing the relevant functions.

The reading head is normally fixed, and the card containing the stripe is passed over it. There are two fundamental ways of passing the magnetic stripe over the reading head:

The user manually draws the ticket across the head, either by “swiping” or by insertion and withdrawal. This is guided by an aperture or channel. While this is commonly used in many other sectors, it is rarely used in the passenger transport sector.
A motorized unit draws the card into the reader and over the reading head at a suitable speed, and then returns the card to the customer. This ensures that the ticket is fully inserted, and properly read. Almost all readers in the passenger transport sector use this principle.

The reading head can be either read only, or read / write. In practice, virtually all devices used for fare collection in the passenger transport sector are equipped with read / write heads, even if the fare products only require the card to be read.

The main internal features of a magnetic stripe reader are:

the reading head
the card transport mechanism
the reader’s microprocessor and its embedded programming
power supply
connectors and data exchange ports

These are packaged in a housing appropriate to the type of fare product and the actions required of the user. The package would normally include:

a display to give information to the user (balance remaining, ticket type, fault type)
LEDs or other color-coded visual display to indicate successful or unsuccessful validation
audio signal to indicate successful or unsuccessful validation, or in some cases to indicate fare product type (e.g. adult or child ticket)
optionally, a printer to print validation and usage data to the ticket
optionally, buttons for the user to select among tariff or fare zone options

Depending on the configuration, the reader may be:

fully self-contained with all of the required software for processing fare products, the fare tables, and memory to store the transactions, and a mechanism for the transaction data to be downloaded
merely a reading device, connected to a “master” device such as an ETM, which holds all of the fare collection software and data, and which receives and stores all transaction data
a hybrid, where some of the functionality can be done by the reader, but it still needs to communicate with the master device for baseline data and to send the transaction record after processing

Magnetic-stripe ticketing technology was dominant in the passenger transport sector through the 1970’s and 1980’s. In the past decade, though, magnetic-stripe technology for fare payment is becoming obsolete as it has by and large been displaced by smart-cards and applications on personal mobile devices.

Transit agencies that have switched from magnetic-stripe tickets to smart-cards have often retained the magnetic-stripe technology in parallel. This is mostly for low-value and disposable fare products, where the cost of a smart-card makes it unattractive to use for such purposes. Sometimes this is part of the transition period, as fare products as gradually migrated from magnetic-stripe technology to smart-cards. In others, it is seen as a permanent solution, although the magnetic-stripe technology may finally be phased out when the equipment reaches the end of its useful life and would need to be replaced.

Read-only applications are mostly required for:

Travel passes, both time-period and personal (employee, concessionary). The reader needs to verify that the ticket is current, is being used correctly (time of day, mode, location, etc.), and to record the transaction data for planning, administrative or reimbursement purposes.
Single-journey tickets, which have been issued and stamped elsewhere and now need to be validated for use on the current vehicle (e.g. on feeder services). The reader may also record the transaction data for planning, administrative or reimbursement purposes.

In practice, “read only” transactions usually involve read / write, even though there is no adjustment of the fare product data or decrementing of value. The reader will usually write data concerning the current validation to the stripe – e.g. date, time, route, boarding stage / zone. This may be used for subsequent boardings to identify linked trips, either for fare collection purposes or to assist network planning.

Benefits of magnetic-stripe readers are:

Facilitates the use of magnetic stripe tickets for a wide range of fare products.
Supports automated transfer validation.
Can integrate with other in-vehicle and at-station devices.
Provides a moderate level of security.
Transaction data can be generated, with extensive downstream potential.
The technology is used widely; it is supported by international standards.

Cautions with regard to magnetic-stripe readers are:

The technology is increasingly becoming obsolete for fare collection in passenger transport.
Cannot support secure electronic purse.
Machines need to be purchased and maintained.
Readers are rather expensive.
Consumables such as printer cartridges can be expensive.
The machines have many moving parts and complex electronics; this requires technical capacity of the operator, and has more risk of failures.