For more transport chat, join our popular Facebook group, Londonist Roundel Ramblings.
Causing a pile-up at the ticket barriers? It's probably due to one of these 137 errors.
A Redditor recently posted this TfL chart, denoting all the potential gate error codes, which mean you shall not pass.
'Too long on journey', 'Always to be rejected', 'Wrong direction', 'Illogical interchange'... who knew there were so many ways your Oyster, ticket or credit card could fail on you?
We're pretty sure we've been guilty of 'invalid geography' before now, especially after a couple of pints.
Actually, if you look closely, there aren't quite 137 errors. 'Illogical interchange (illogical route)', for example, crops up three times (which seems illogical to us):
A similar list, available from an FOI, also includes actions for staff to take on the various error codes.
Our favourite without a doubt:
Description: Ticket unreadable
Comments: Possibly upside down
Action: Try again
With thanks to the Redditor for their permission to use the image.