The following points emerged from an interview on France24 with a Spanish rail engineer:-
- The train did not have an automatic braking system going through this curve.
- An automatic system - the ERMS - is used on the long stretch from Ourense to Santiago but not for the last 3-4km.
- An automatic system monitors a train continuously and stops the train the second it exceeds the correct speed.
- A non-automatic system only monitors the speed as the train goes past sensors.
- The curve exists because it's close to a residential area. Such curves are not uncommon when high-speed trains come into cities. As it's unrealistic to avoid them, it's essential to protect passengers via an automatic braking system. This was not in place at this curve.
- Railway accidents rarely have just one cause. Usually there's a series of them.
I'm not clear why/how a train could have an automatic system for part of its journey and then only a non-automatic system once it enters urban areas. Perhaps someone could explain. I'm assuming that the infrastructure wasn't in place on the tracks.