There are now enough daylight pictures (
e.g. on the BBC» ) to confirm some of what was "known" but confusing last night.
The eastbound
GWR▸ train (1F27 ) passed Salisbury Junction first (timed 18:41 - 5 minutes early). This is a sharp right turn, limited to 20 mph. For reasons still unclear, this train was held at Dean (some distance before the station) for over two hours before departing 151 late and being cancelled at Fratton "Reason TY [Mishap-Train Operating Company cause] ".
The westbound GWR train, subject to the same 20 mph speed limit round the sharp left turn, was timed at Salisbury Junction at 18:42, 19 late. It stopped with the last vehicle outside the tunnel, and still on the points. Its rear end was thus well to the left of the Down Main Line that 1L53 was arriving on. This last vehicle was reported to have derailed, but I think that might be a mistake. It was struck soon after so ended up derailed anyway, and it does seem unlikely that an obstruction would derail only the last vehicle - and it never entered the tunnel. We'll have to wait and see on that one.
The
SWR» train (1L53) had earlier been cancelled before departing "Reason JP [Failure to maintain vegetation within network boundaries in accordance with prevailing Network Rail standards]". It was reinstated and was last timed departing Andover at 18:30, 6 late. It should have passed Salisbury Tunnel Junction at 18:39, so with the delay would be expected at 18:45 (any time in
RTT» is interpolated). Its straighter run over the points allows a 50 mph speed limit, but it should have been slowed, delayed, and then stopped by the signals. The biggest question at the moment is why that did not happen.
We know 1L53 bit not stop, and struck the rear vehicle of 1F30 a glancing blow. It is not possible to tell from the resting positions where that stopped carriage was when struck, but in its current position the two trains would not have passed to strike corner to side. The impact would have been corner to corner, and much more violent as a result. Either way, the leading end of that GWR vehicle was did not pass the tunnel portal; it's not clear from the picture whether it lodged against it and could go no further. 1L53 was thrown off its track, and half overturned, and ran into the tunnel in that canted position along the Up Main and (at least in places) became wedged between 1F30 and the tunnel wall.
Two things went well in the accident, accounting the the relatively light injuries, and to only a small number of passengers and staff. One was that the body shells largely kept their shape and bounced off each other. The other was that no fire broke out. It could have been very much worse.
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