(sorry I've not quoted the varus things people have said prior but it'll take too long)
With regards to signals on the line, from a report I saw previously about something which happened at Sudbury a few years back, there is a track circuit at Sudbury, which has to be activated before clearance (by phone I believe) is given for a return working (came up as part of the wiggly wire thread)
I guess if you were going to be picky you could say that a sensor could be on the crossing which alerts the driver by wireless signal, but again the cost would be prohibitive for the likelyhood of there been a problem when a safeguard is already in place (by means of the crossing phone)
With the line being closed - as it is only single track there is no way to bypass the area and I with it only being a short branch, may be seen as less of a priority than a major arterial line would for reopening.
How long did it take for the line up in Scotland to reopen after the derailment the other week?
With motorway closures, only today the M1 southbound was closed for over 8 hours (04:45 - 13:30) due to a fatal accident involving 4 lorries between Jn 15 and 14 so it does happen. I would think aside from evidence gathering with is obviously a necessity, access would also play a part in recovery time. A number of railway lines are pretty remote and trains are also heavy whereas road vehicles can be relatively easily recovered and are, by their nature, accessible, and so can be (even if only partly while repair works to the road are carried out) reopened or diversions put in place via minor roads etc - rails are going to take longer and cause more disruption
From the BBC News story, it appears the tanker has already been recovered but the train needs a 100 tonne crane which will be on site at a later time.
As with everyone else though, I wish the injured a speedy recovery, especially the driver and the passenger who seem to have been the most seriously injured.
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Taken from the BBC Video footage they have...
It amazes me sometimes what can be repaired.
When you look at the damage the tree did when it hit the HST the other week, it looks pretty hurrendous. Yet, since it doesn't appear to have damaged the major loco structure, within a few months (well, maybe

) it will be back out again looking as good as new!