This is actually a very hard problem!
The message you selected appears as a TfL status, but it starts it’s life as a railway system status (Darwin).
587 a road vehicle colliding with a bridge
WST Wood Street station
The control room for London Overground (operated by Arriva Rail London at Finchley Road) sends this information to the TfL control room, along with their decision about which segment of the several Overground Lines is to be closed. Here it’s Hackney Downs and Chingford because trains can still run between Liverpool Street and Hackney Downs. Note here “No Service”.
ARL also report “Severe delays” - as this has a very specific meaning (the operations service level agreement with ARL) to the rest of the “West Anglia” London Overground line “Liverpool Street and Cheshunt / Enfield Town” as this is their line-based system.
" London Underground accepts their tickets via reasonable routes." is always true during any disruption.
However, I think from observation that the messages posted to the status system are … human mediated. This is because working out which sub-line segments are affected. See…
The problem (and this applies to (MTR) TfL Rail too) is that when a non-tube line is blocked by an incident, working out if and where a service can still be run depends on the locations of “cross overs” where the trains can be terminated short and reversed.