How do departure boards work?

[talltim]

an example.
I was at Sheffield yesterday waiting to catch the 17:05 Northern service to Nottingham. When I got to the platform at about 17:00 it was the next train on platform 6A and on time. The board then changed to the late running 16:54 XC service to Plymouth (or somewhere down that way) which was due at 17:09. It got to 17:09 and the expected time kept going up a minute behind the actual time. Eventually the on time 17:23 XC service came up on the board, before reverting the 17:05 Northern service which actually arrived at about 17:19.

So, where do the 'Expected' times come from? Why did however programmed the software not realise that it just looks stupid saying that the train will be here 2 minutes ago?. When the train is on time the departure time is shown, however once it is late it seems to show the arrival time, is this correct?
Also, when a train is shown as arriving in minus 1 minute, then it can't be far away, right? So then how does the train then take a further 10 minutes to arrive? Lastly, the main departure board showed the 17:05 as running later than the 16:54 until the very last minute, when the order changed. As AFAIK there is nowhere for a train to overtake between Meadowhall and Sheffield the Northern service must have been ahead of the XC for at least 5 minutes and if the XC had been less than a minute away for 10 minutes how does that work?

 

[Aictos]

Many CIS systems work off a number of sources including TRUST but also Track Circuits which automatically displays if the train is on time, late or even cancelled.

I hope that explains things better?

 

[causton]

Why oh why has nobody made a function that automatically makes the expected time at least the current time, or in the future?

And of course they aren't perfect, looking at some departure boards for FCC one service says it was late a few minutes at Harringay, and showed something like this
Harringay Timetabled: 17:03 Actual: 17:05
Hornsey Timetabled: 17:05 Actual: On Time
which obviously cannot be in any way true!
The station after had the actual 2 minutes later as well

 

[wintonian]

It gets really annoying when it announces that the train to X is approaching the platform when the train to Y is standing in it. :roll:

 

[jopsuk]

Presumably if we ever get to ETCS Level 3- full moving block signalling- departure board onformation will be able to be very accurate, including good estimates of exact arrival time, as it requires speed and position (to a reasonable level of accuracy*) to be known at all times.

*we're not exactly talking Heisenberg here.

 

[144022]

they can use mill race to get a faster running train past a stopper

 

[Eric]

It gets really annoying when it announces that the train to X is approaching the platform when the train to Y is standing in it. :roll:

Or they announce that train to X is approaching the platform and it's nowhere to be seen, only then for at the very last minute a platform alteration announcement for the train to X.

 

[wintonian]

Or they announce that train to X is approaching the platform and it's nowhere to be seen, only then for at the very last minute a platform alteration announcement for the train to X.

Or also in my experience stand up and gather your luggage only for some bl**ding bit of freight to zip past.

 

[talltim]

they can use mill race to get a faster running train past a stopper

Do you mean the loop the 142 is on in Google Maps? I've never seen a passenger train in them, but obviously it does happen!

Of course in my case it seemed to be a slower train that overtook a faster one. (and stayed ahead out of Sheffield, even though it stopped at Dronfield)

 

[SWT_USER]

Quite funny at Barnes in the mornings when as the train is pulling in they announce a platform alteration from 1 to 2 causing a lot of commuters sprinting down the platform over the footbridge and often missing the train.

 

[monkey]

Or they announce that train to X is approaching the platform and it's nowhere to be seen, only then for at the very last minute a platform alteration announcement for the train to X.

...this happens at leeds regularly, it really is farcical - leeds station is just mess. Its really difficult if you have heavy luggage to get upto the footbridge and down again (especially as they only have escalators going up). few weeks ago from leeds to manchester (arriving from hull) even while it was on the other platform the anouncer was still announcing it was on the platform we were on a, we just instinctively all ran, cos we could see the train on the opposite platform and continued to do so until it left...

Also at york I've I've noticed regularly they announce the train as arrived even when it is nowhere to be seen for around ten minutes...