What happens to ticket barrier data?

[krus_aragon]

Wow, that's huge compared with the 20 characters I was once told!

A bit is just a 0 or a 1. You need to string seven or eight bits together following an encoding scheme (such as ASCII) in order to store characters. So 20 characters at 8 bits each would take up 160 bits.

20 characters wouldn't be enough to name the origin and destination stations, but the magnetic strip is read by a computer, which will be just as happy with numbers. 12 bits will store a number from 1-4096 (as mentioned above), so having given 24 bits to origin and destination stations, any ticket barrier can use a local database to know if that ticket is valid to start, break, or end a journey.

You could assign a 25th bit to show whether a journey has been started (to be set by the barrier at the origin station) and another to indicate whether it has been finished or not.

Dates for start and end of validity could be stored in as little as 12 bits each (depending on how far into the future you want dates to go), and then you can go on with other details you want to record. I seem to recall that a ticket can be issued for up to eight adults and eight children. That'd be another six bits (2 to the power of 3 is 8 adults). Then there's railcards, etc., and the magnetic strip still isn't half full...

(This is all deduced from principle, and not based on the actual specifications.)

 

[ralphchadkirk]

Why would there be a time limit on keeping data if, as widdle says, the ticket number is not recorded and therefore there is no connection to the ticket user?

So that the machines memory does not get clogged up...?

 

[radamfi]

So that the machines memory does not get clogged up...?

The implication was that data had to be deleted to comply with legal requirements, such as data protection legislation. I didn't think that would apply if personal information is not kept.

 

[142094]

Not sure if this applies to all stations with barriers but assuming it does, I was told that the main information used at Leeds is the number of tickets going through the barrier and in which direction. Therefore this data can be used to guage demand in the peak times and how many barriers should be open for those exiting the station and for those getting onto the platforms.

 

[barrykas]

So it probably takes at least 4 bits to store each character if each character of the NLC code is stored on the ticket separately (2 to the power of 3 is 8 and 2 to the power of 4 is 16. You need 10 possible combinations of 0s and 1s to make a binary representation of the numbers 0 to 9). Which would make it 16 bits per station.

The Origin and Destination NLCs are stored in 15 bits each. 5 bits for the first character (00 to 31, allowing for the digits 0 to 9 and letters from A to V) and 10 bits for the last three digits (000 to 999).

Cheers,

Barry

 

[dan_atki]

If they were using the ticket again.

I'd certainly hope any ticket inspection on the train would enquire as to why the ticket was being used in the wrong direction...

 

[MikeWh]

It is stored for up to 7 days on the terminal
Once downloaded it can be stored for up to 28 days
After 56 days the data MUST be deleted
The summary may be retained for up to 5 years

This ties in with the Oyster journey history only being available for the last eight weeks. What I don't understand is why. What is the legal reason why this data cannot be made available for longer?

 

[ralphchadkirk]

This ties in with the Oyster journey history only being available for the last eight weeks. What I don't understand is why. What is the legal reason why this data cannot be made available for longer?

The Data Protection Act requires that data is kept no longer than is necessary.

 

[OwlMan]

The Data Protection Act requires that data is kept no longer than is necessary.

How does the Data Protection Act apply? - there is no personal data involved.

Peter

 

[ralphchadkirk]

Quite correct. It was 6 o'clock in the morning though!

 

[wibble]

So does each separate barrier have its own database or are they all linked to one station, regional, TOC or even national database? How much data can any one barrier hold (more than 24 bytes I assume? )? Similarly, how much data can Oyster cards hold?

All the gates are linked to a central computer at each station which stores the data. Each TOC will have access to their own gateline's data. e.g. Southern would have access to Victoria's gate data but not Euston's.
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On a related note (though don't get me started!) usage statistics even using printed ticket data are next to useless, given how many people use zonal or other season tickets - and especially given how many ticket issuing staff completely ignore what you ask them and issue a ticket to alternative stations if the price is the same and they think it's easier.

That's not true - the data can tell you:
- What ticket types are arriving/departing a station during the day
- It acts as a check to see if the gates are rejecting or accepting tickets they shouldn't be.

 

[mickey]

- It acts as a check to see if the gates are rejecting or accepting tickets they shouldn't be.

Well in Liverpool all gates (except at Lime St) are set up to reject anything other than local single/return tickets - season ticket holders are forced to queue for the manual gates (for no obvious reason, I might add). However, my point in this case was that neither method for aggregating numbers of passengers using each station is particularly good, though I accept that counting the number of passengers in each direction (as per 142094 above) is a good use of gate data.

I'm in full agreement about the usage stats, but I;m a vit confused about the last bit of your post! Can you give some examples?

Fares to Port Sunlight and Bebington are the same (from both Liverpool and Chester directions) so if you ask for a ticket to one you're invariably given one to the other. Similarly with Wallasey Village, which must have artificially low usage stats as staff at Liverpool stations will *never* issue a ticket there - they always use Grove Road (presumably from the days when they had short cut keys for common destinations?).

It's not just a Merseyside thing either. Try getting a ticket to/from Dove Holes and you'll find it's always given from/to Buxton - and in this case it's particularly depressing as low usage stats here are much more likely to be used as an excuse to cut back services.