Without wanting to derail the thread too much, can someone explain why freight train derailments appear to be more common than passenger services?
Freight train wagons of the type used for this train or similar are significantly heavier than passenger coaches/cars/carriages. Even with reinforced concrete sleepers, if there is even a tiny bit of wear in the rail and the fixings, the rails move (are pushed) outwards slightly during the normal passage of these trains.
So, if the track is not to a sufficiently good standard, and the rails move too much (spread), a wheel could drop off the inside edge of the rail. Or the rail may be able to twist (rotate) also causing a wheel to drop into the four foot.
To help prevent this, the running surface of wheels on some types of heavy wagons are wider.
In my area, it’s the china clay train that used to cause us problems.
Of course there are other issues. The only human on board is normally the driver. So no one else to hear any unusual sounds, and take action.
And if a problem develops with a brake, wheel or coupling, again, unless a signaller, station staff or other staff working lineside notice something amiss, again it may develop until failure occurs.
There are hot axle box detectors, but these are not able to detect other defects.