Oystercard: Not Guilty

Oystercards have been available in London for the last two years. I think I was one of the early members of the London travelling public to get one – replacing my annual Travelcard with an Oystercard in early 2003. Now Transport for London (the department of the Mayor of London’s office that looks after London’s public transport systems) are really marketing the card very heavily – on the basis that it costs less to provide general ticketing, is more secure against fraud, is more efficient in terms of speed of boarding buses than using cash, gets you through the gates quicker on the tubes and also does clever things like ensuring that you never pay more than you should if you made several separate journies in one day that would otherwise have costed you more if you’d bought paper tickets each time than if you had bought a one-day travelcard. (Hope that last sentence made sense.)

Anyway – the Oystercard is based on RFID (Radio Frequency IDentification) technology – which means that the card itself has a chip and antenna embedded in it – which gets irradiated by a reader when you bring it close up – which causes two-way communications to occur between the card and the reader. Which means that the Oystercard can hold your travel tickets for your season-ticket transport zones – but can also hold “prepaid” units of cash for ad-hoc trips outside the zones permitted by your season-ticket. You don’t have to actually “touch” the card to the reader – it’s a “contactless” technology – but you have to bring it up pretty close – and many people just keep their Oystercard in the characteristic blue Oystercard wallet that comes with the card – which in my case I also use to carry my credit cards, bank debit cards, car breakdown-rescue card, business cards etc. etc. – and you just touch the wallet against the reader – and hey presto – within the a fraction of a second the wonderful data exchange process occurs – and the gates open to let you through on the tube – or the box on the bus bleeps to let the driver know that you’ve got a valid ticket and you just walk right in.

My Oystercard
(Pictured on top of the tatty Oystercard wallet that I carry it in.)

It’s all really great stuff – and I haven’t really had any problems opening the gates on the tubes or getting on the buses. Until recently. I discovered a problem that the designers of the system hadn’t really thought about when conducting their customer use cases: Buses can sometimes get stuck in traffic – and people can sometimes get off the bus to walk instead – and people can sometimes get back on the same bus they got off.

They never thought about this particular use case.

It was a really hot, sticky evening travelling home the other day – and the Route 79 bus I got onto at Alperton was crawling up Ealing Road sooo slowly that I could walk faster than the bus – even if I walked slowly. And given that it was sooo hot and sticky on the bus – I decided to get out and walk – at least there would be some fresher air. I decided that I could walk it up Ealing Road – towards Wembley High Road – following the exact route of the bus – and pick the same bus at the main stop on Wembley High Road. I figured that loads of people would get off the bus there (meaning less congestion on the bus)- and that also happens to be the point at which the traffic congestion gets better – and the bus, therefore, gets faster (meaning that the air on the bus circulates better), and I would lose no additional time getting home.

So that’s what I did.

Only when I tried to get back on the bus at Wembley High Road – the Oystercard reader on the bus bleeped an ALARM message at me and the driver.


The driver asked me to touch my card against it again. So I did. ALERT: PASSBACK ATTEMPTED. I stood there wondering what’s going on. He sat there wondering what was going on. He’d never seen that alarm before. In the end he just shrugged his shoulders and let me on anyway.

I spent the rest of my bus journey home contemplating. What did “PASSBACK ATTEMPTED” mean? In the end – I decided that the designers must have figured that if someone tries to use the same Oystercard, on the same bus, within a certain time-period – then it should be handled as a “fraud” alert known as “Passback” – which presumably means that the someone used the Oystercard to get on the bus – and then tried to pass-back their Oystercard to someone else in the bus queue so that an accomplice could get on the bus too. Sounds fair enough to me – but, as in my own case, there are some perfectly innocent and legitimate scenarios that look like “Passback”.

I consider this a design flaw – or else a known issue that was too expensive to resolve – so they decided to live with it – especially as the occurrences of legitimate use would be quite rare. (As in my case of getting off and back on the same bus in the space of 10 minutes or so.)

The irritating thing though is this: the system logic in this particular part of the decision-tree supports a business policy that assumes that you are Guilty Until Proven Innocent. That’s not nice.

Not nice at all.

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