We are all familiar with barcodes, especially the Uniform Product Code used in supermarkets since the 1970s. It is called a linear barcode because the bars run in a single direction. The depth of the bars makes for speedy reading but adds no extra information to the code.

We have also become familiar with the use of barcodes in transport ticketing, especially in air and rail. Although in some simple cases a linear barcode can be used for transport ticketing, in general 2D barcodes are used as they can contain much larger data loads. Although the term 2D barcode is often used interchangeably with QR Code in transport ticketing, this is a common mistake and there are other 2D barcodes in use.

PDF417, defined in ISO/IEC standard 15438:2015, is a stacked linear barcode format. "PDF" stands for Portable Data File. The "417" signifies that each pattern in the code consists of 4 bars and spaces in a pattern that is 17 modules long. Since the early 2000s, airlines have been using an IATA 2D barcode standard for boarding passes. It originally used the PDF417 standard, but has now been extended to include the AZTEC standard.

The Aztec barcode is published as ISO/IEC standard 24778:2008. Named after the resemblance of the pattern to an Aztec pyramid, the barcode has the potential to use less space than other matrix barcodes because it does not require a surrounding blank "quiet zone". It was found to be quickest to read in railway carriages where both the barcode and the reader are swaying.

 

 

The QR Code (abbreviated from Quick Response code) is a type of 2D barcode first designed in 1994 for the automotive industry in Japan. It is published as ISO/IEC standard 18004:2015. As well as logistics, industry and transport, QR Codes are now being used in the payment industry, including WeChat Pay and Alipay. EMV has published specifications that support payment methods using barcodes.

There have been some moves to introduce 3D barcodes, using embossing or colour to provide the third dimension. So far, these barcodes have not entered the consumer market, where 2D barcodes predominate on mobile phones and meet the business need.

Use of barcodes in Transport Ticketing

Barcode ticketing in transport has been around for about fifteen years. When it was introduced, it provided a challenge to transport smartcards as a method of fulfilment and was castigated as being obsolete technology. Despite that, it has been growing ever since and now has become ubiquitous in some sectors, for example in rail ticketing worldwide. A major advantage of barcode tickets compared to smartcards has been the ability of the passenger to see what the ticket details are. This is very important where a reservation has been made or the ticket is for a timed train.

Barcode ticketing has taken two approaches, depending on the business function. In some cases, such as high-speed rail where on-train ticket inspection can be linked to an online ticket manifest, the barcode only needs to contain an ID for the passenger, such as the booking reference or PNR. In others, where access to the back-office system is less certain, the barcode can contain all the key details of the ticket, including reservation details such as train, coach and seat data.

The move to barcode transport ticketing coincided with the deployment of 2D barcodes, as the larger data capacity and error correction was well suited to ticketing applications. Although barcodes can be copied, they often will contain a digital seal in addition to the ticketing payload. The digital seal provides protection against counterfeiting, for example fraudulently changing the date of travel in the barcode.

With barcodes there is no need to distribute customer media and in consequence barcode ticketing has been significantly cheaper to implement. Barcodes also benefit from the move to asymmetric cryptography, which allows for cheaper readers as they only need to hold a public key. Transport smartcards conventionally use symmetric cryptography which requires secure devices to be embedded in all readers to keep the keys private.

Copying is always identified as a weakness of barcode ticketing. In some implementations a visual security device has been printed/displayed together with the barcode. This could be a picture that contains ticket data such as passenger name or journey itinerary, or it could be a difficult-to-fake dynamic watermark. Gates are programmed to reject ticket duplicates but the emphasis is now moving to scanning linked to an online validation back-office and with duplicates being deny-listed when scanned. In the UK, RSP has defined standards for the barcode ticket and for the interfaces between readers and a federated system of validation back-offices. In Europe, the UIC (International Rail Union) has done the same job and their standards will be part of a regulatory framework for rail ticketing defined by the European Rail Agency.

It has been argued that barcode readers at gates are not sufficiently fast, especially in high-throughput stations. This may have been the case with paper barcodes, but it is different with barcodes on mobiles. Indeed, even TfL has mooted the possibility of barcode readers at some tube stations, providing the end-to-end functionality needed for a national rail barcode ticketing network.

It is possible to use the embedded functionality in Android and IOS handsets to display barcode tickets, combining the visual information for the passenger together with the barcode used by gates and readers. However, transport operators are tending towards dedicated barcode generators, stored securely on the mobile phone. This allows for the generation of the barcode offline by the mobile itself, independent of the original ticketing engine. Such barcode generators allow for very short-term barcodes to be used, providing another protection against copying. Latest developments include ECC (elliptic curve cryptography), which is more efficient than the current RSA technology. Examples are being developed by SNCF (France), VDV (Germany) and ENTUR (Norway) and it is hoped that all these developments can be harmonised into a single European standard.

 

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