RealTimeTrains "not stopping"

[arb]

I've been watching particular trains on RealTimeTrains all of this week, specifically those leaving Cambridge just after 7:00am. Whilst doing this, I've noticed that the 0652 train to Kings Lynn (which starts from Kings Cross at 0543) has been shown as "not stopping" at Cambridge every day this week. Today's specific example is at http://www.realtimetrains.co.uk/train/G43243/2016/02/05. Looking back through previous weeks I see that the same is true the vast majority, but not quite all, of the time.

I understand that there are various reasons why a train might not call at a station it is scheduled to, but this particular example seems to be happening on the same train at the same time far too frequently for me to accept that as an answer! Equally, I know that there can be glitches in the data gathering used by RealTimeTrains on occasion, but again it seems highly unlikely that that would affect the same train at the same time day in, day out.

Does anybody know whether this train really does not stop at Cambridge on a regular basis, or whether it's a glitch in RealTimeTrains and if so, why that glitch happens so reliably with this particular train?

 

[Kite159]

I notice something similar happens with southeastern services which get "not stopping" entries at Sevenoaks.

 

[eastwestdivide]

If you switch to advanced mode, it shows scheduled arrival and departure times, but the actual arrival is "pass" while actual departure is a proper time.
Maybe something to do with long platforms and two trains in platform signalling arrangments?? i.e. iIt records "passing" the nearest end of the platform and therefore not stopping, but then records departure from the further end of the platform. Other wild speculation may be available.

 

[jnjkerbin]

Yes, I contacted them about the Sevenoaks issue a while ago, and was told that because the system works by taking the time the train passes the signal before the station and adding a delay to that, if the delay is off, then it is possible that the system believes the train arrived at the same time or after it departed.

 

[Tom]

jnjkerbin has the right answer. There are a load of updates to the offset database waiting to be uploaded to the main system at the moment but with the recent physical move of RTT and the servers to its new York hosting location, and subsequent launch of RM, it's been on a bit of a backburner.

Cambridge is an artefact of how it is laid out and the through platform. I've yet to work out a half decent way of sorting that one out. I suspect louis97 or myself will have to make a visit and spend a few hours watching and measuring train movements to sort that one!

 

[OxtedL]

The explicit issue here is presumably that trains departing from platform 1 often pass through platform 4 on their way north, but trains can also pass straight through platform 1 and stop at platform 4, and the system has not yet been taught how to work out when the former has happened rather than the latter.

 

[ld0595]

I've had this on a few East Coast services from Inverkeithing when they're running slightly behind schedule. I got on one once and checked RTT which said it wasn't stopping! I just thought it was a glitch or something.

 

[greatkingrat]

The explicit issue here is presumably that trains departing from platform 1 often pass through platform 4 on their way north, but trains can also pass straight through platform 1 and stop at platform 4, and the system has not yet been taught how to work out when the former has happened rather than the latter.

Plus the mid platform scissors crossover to the through line adds even more possibilities.

 

[arb]

Thanks for the replies - the explanations make sense. Having looked at RTT a bit more, it's actually nothing like as infrequent an occurence as I'd thought at Cambridge, and definitely not limited to the 0652. For example, the xx35 trains all the way through the day seem to suffer from the problem as well, and quite a few others can easily be found.

I'd noticed the occasional "not stopping" before at Cambridge, but had always just put it down to random glitches - I'd never noticed the patterns until this week!

 

[OxtedL]

Plus the mid platform scissors crossover to the through line adds even more possibilities.

That is true, although I would expect their system to record real time information for a platform (rather than a through line) if the train passed through one, so that is less likely to cause trouble.