My somewhat buggy website gets a mention... I don't currently display route data in that area.
Here is a link if anyone wants to look themselves.
Taking a look manually at that stored data which I don't currently display on there I can confirm the following from my record of signalling data. Anything in italics I've tried to explain the meaning of after the timeline.
19:33:29 Route
proves from the Up Main to Up Slow at Huntingdon North Junction for 9J61 to enter Platform 2 as booked (pink route below)
19:33:32 Signal 352 displays a
proceed aspect
19:36:50 9J61 passes signal 352 and it displays a
danger aspect
19:37:13 9J61 clears the pointwork at Huntingdon North Junction and the
route releases
19:37:37 Route
proves from the Up Main to Up Fast at Huntingdon North Junction for 1Y90 to continue on the fast lines as booked (red route below)
19:37:41 Signal 352 displays a
proceed aspect
19:40:19 Route set earlier for 1Y90 to stay on the Up Fast cancelled (also known as replacing to danger / pull the signal/road)
19:40:21 Signal 352 reverts to a
danger aspect. 1Y90 is just one signal away at this point approaching signal 356 - if the signal was visible, the driver would have seen it go from green to a single yellow (they would have obviously been warned by the signaller this would happen / requested it as mentioned up thread)
19:41:11 9J61 clears the
signalling section in Huntingdon Plat 2. It might have been a few more seconds before a route could be set due to local
interlocking rules. Regardless an approach locking timer would prevent a route being set into Plat 2 for 1Y90 for usually 2-3 minutes at 125mph (clearly 2 here based on the next timestamp) after the route was cancelled - so possible to set a route from 19:42:19 ish onwards
19:42:34 Route
proves from the Up Main to Up Slow at Huntingdon North Junction for 1Y90 to enter Platform 2 (pink route below)
19:42:37 Signal 352 displays a
proceed aspect
19:42:51 1Y90 passes signal 352 and it displays a
danger aspect, and then enters Platform 2 at Huntingdon
I think this shows some incredible quick thinking. Hats off to the driver, signaller, and anyone else involved in getting the train into a platform as soon as possible.
Annotated screen grab of the state at 19:40:19 when signal 352 when the red route was cancelled and signal 352 reverted to danger.
View attachment 191590
Some further explanations:
For a route to "prove" this means that the points have swung to the required direction and it's detected that they've locked - you don't want them not going all the way or locking and having points move under a moving train! The time it takes for this to happen once the signaller requests a route to be set depends on the pointwork installed but I'd say its usually within the general ballpark of 5 to 10 seconds for an important junction like this. Maybe slightly quicker. From this the signaller acted almost immediatly once the timeout on the cancelled route from signal 352 ended.
Proceed aspect - green/yellow/double yellow. Danger aspect - red. The signalling feed's don't differentiate between different possible proceed aspects.
Route release - unless set as an auto route, the route will "release" and the points will usually/sometimes* automatically move to their normal position once a train has cleared the points. No route is automatically set over them so the signal protecting the points stays red, until the signaller or ARS/DRS sets a route.
The interlocking rules prevent conflicting movements happening. Track is split into signalling sections and if a train is detected in a section or a route set over it the interlocking system prevents any conflicting moves being made.
I have no formal relation to the industry and am just sharing what I've learnt on here, simulating various signalling areas on SimSig, and creating the Vail website linked above. If anyone who knows the area better and has any corrections to make please let me know!
*Some points will auto revert to normal position (Up Main -> Up Fast in this case) but I have no idea how widespread this is. It might be standard on most points in the country everywhere or not, I don't know and it's very niche stuff so I haven't been able to figure it out from a quick google.
It's near Stilton Fen / Holme on the two track section just south of Peterborough. Huntingdon was previously controlled by Kings Cross PSB before moving to York ROC.