[pjc50]

So, we don't know if this is the case, but one way to do this is not to ask the phones but the cells. The mobile network has to know where the phones are by cell; the cells are often small relative to the speed of the train; there are also cells installed specifically to improve service on trains, or provide a base station to the train wifi, or for communications to railway staff.

If you get a bunch of phones switching cell near simultaneously, you can tell that a train movement across the cell boundary has probably happened. Then correlate that with the other data feed about train blocks, and bob's your uncle.

Only about 50% of trains have wifi: https://www.businesstravelnewseurope.com/Ground-Transport/UK... ; but it's easy to imagine getting the mobile hotspot on the train to share its GPS location as well.

[munk-a]

You're missing the fact that the system is also divided into explicit signal blocks and those blocks do report train presence to a centralized system[1]. I am not certain if they want to share that information, but if someone got serious about building a system like signalbox I'd expect that NetworkRail would either offer their data, a degraded version of their data on a lag for security reasons, or consider those security reasons so serious that they'd attempt to prohibit deriving that data from cell signals.

1. Mostly, some signal blocks are still entirely manually managed but, IIRC, at this point those manually managed segments are low traffic areas where only one train is allowed into the block group at a time even if the old signal management systems would allow multiple trains.

[ButlerianJihad]

Before he was hired by a San Diego-based defense contractor, my maternal grandfather worked on the railroads as a pipe-fitter, and he designed and built for me a high-quality Lionel model railroad in his home, before he passed away. It even had those little smoke-generating tablets that you could drop into the smokestack. I was only six years old.

This year, I was curious about whether I could track freight trains in my region or nearby, in real-time, and perhaps more details like what sort of cars were linked in the train, how many locomotives, what sort of freight they were carrying, etc.

After a few fruitless searches for this tracking info, I realized that the same info that would be "recreational" for me would be "operationally valuable" to any domestic terrorist cell or motivated insurrectionist, as well.

Trains derail all the time, we are told, and trains are robbed blind increasingly often, so I am sure there is some sort of illicit/underground tracking that takes place already, but for now, I must content myself with noticing trains using my own eyes and ears. The freight line next door is inhibited from sounding their horns except in emergencies. And thankfully, I find freight-train and light-rail noise to be calming and soothing, even at 3:30am...

[marksomnian]

That data is in fact made publicly available by Network Rail: https://wiki.openraildata.com/index.php/TD

though interpreting it isn't the easiest thing in the world...

[munk-a]

That is fair - though at least they've well defined their standard. It'll be easier than trying to parse that data out of HTML with regexes at least.