1B15 PAD - SWA on 25/8/25

[snowleopard]

Hi,
a relative of mine was on the 12.48 London Paddington to Swansea (1B15) service today. After a near punctual start, it lost 10 minutes or so approaching Reading. So far so good, the official delay explanation on Journeycheck etc. was that it was affected by earlier signal failures today.

However, what amazed my relative was that after Swindon, the delay kept ticking up at every station (https://www.realtimetrains.co.uk/service/gb-nr:P08245/2025-08-25/detailed indeed shows the train increasing its delay at nearly every other passing point) - ending up in a not so great +39 on arrival in Swansea. I was asked what would explain the slow deterioration from +12 to +39 over the course of the journey. The best I could come up with was a likelihood of line congestion from the said previous signal failure or perhaps being stuck behind a slow stopping train, but does anyone know more/better? A very quick look at Cardiff/Newport departure boards didn’t show any other such significant delays so I’m wondering if this train just got unlucky?
Thanks in advance for any explanations or informed guesses that I can relay back…

 

[Earle Grey]

Ended up following 4V44 1044 Daventry - Wentloog from Uffington to almost its destination, and then caught a stopper 2B69 1451 Cardiff Central to Swansea up from Briton Ferry.

 

[Topological]

This is the reason it would be great to have a 4-platform Port Talbot Parkway so that the Swanline could let the GWR overtake (it might even be possible to just use the two platforms (depending what needed to come the other way).

The number of times the GWR ends up following a Swanline with no chance to overtake is very high.

That is all for speculative, but this 1B15 case is far from a one off.

 

[Earle Grey]

The number of times the GWR ends up following a Swanline with no chance to overtake is very high.

You'd think so, but given the dwell time between London services is 50 minutes or so at Swansea and up to an hour at Carmarthen, I dunno but can't see that happening.

By the way 1L28 1622 Swansea to London Paddington, the next working off 1B15 - left on time, well 45 seconds early if you are watching on RTT. Delay endth.

 

[snowleopard]

Very helpful, thanks both! That is in line with what I suspected and I guess inevitable (on current infrastructure). A bit tricky when you have a prebooked taxi waiting at the other end and need to keep correcting your ETA with apologies. I wonder how far off we are from AI being able to calculate that “Because we were 10mins late in [Reading], we’ll now be behind a freight train and then behind a local train so we’ll end up being 40mins late in [Swansea]” and translate that into realistic ETAs on journeycheck etc. from the onset of the delay - rather than pretending ETA will also be +10. I guess factoring in all the hypothetical events that could arise down/up the line would make this v. complex though.

 

[Topological]

Very helpful, thanks both! That is in line with what I suspected and I guess inevitable (on current infrastructure). A bit tricky when you have a prebooked taxi waiting at the other end and need to keep correcting your ETA with apologies. I wonder how far off we are from AI being able to calculate that “Because we were 10mins late in [Reading], we’ll now be behind a freight train and then behind a local train so we’ll end up being 40mins late in [Swansea]” and translate that into realistic ETAs on journeycheck etc. from the onset of the delay - rather than pretending ETA will also be +10. I guess factoring in all the hypothetical events that could arise down/up the line would make this v. complex though.

From the Cardiff departure time it is possible as there is no overtaking.

Cardiff is something of a randomiser though so I do not make any assumptions until the order of departure from Cardiff is confirmed.

Don't need an AI though, simple maths will do the job

 

[AndrewE]

From the Cardiff departure time it is possible as there is no overtaking.

Cardiff is something of a randomiser though so I do not make any assumptions until the order of departure from Cardiff is confirmed.

Don't need an AI though, simple maths will do the job

Maths? It's just logic and arithmetic!

 

[snowleopard]

Yes, the reference to AI was slightly tongue in cheek, as everything seemingly has to be labelled AI to get traction/funding these days…