In Andalusia, Spain, two trains derailed causing 41 victims and over 150 injuries – although the toll could worsen further in the coming hours. The accident occurred around 7.45pm on Sunday 18 January, near Adamuz, near Cordoba: involved in the disaster were a first train of the Iryo company, headed from Malaga to Madrid, and a second train of the Alvia service, which collided with the first convoy and then ended up in a four-metre embankment.
At the moment the exact causes of this disaster are not yet known but, as we will see, it seems that the most plausible ones are due to failures of the train or railway infrastructure.
The reconstruction of the train accident in Adamuz
We are in Spain, in Andalusia, more precisely near Adamuz, a small town with less than 5000 inhabitants. To the north-west of this small village is the railway line, made up of two tracks: one for trains going north, and one for those going south. That evening, as we said, there were two trains on that stretch.
The first was an Iryo 6189, a high-speed train traveling from Malaga to Madrid with 284 people on board. The second train was an Alvia 2384 which left Madrid and headed for Huelva, in southern Spain, with 187 people on board. It seemed like a quiet evening, like many others, but unfortunately at 7.45pm, disaster struck.
The passengers on board the Iryo feel a vibration, then suddenly darkness and a loud noise. Witnesses say they were thrown, without knowing what was happening. What they still didn’t know is that the last carriage of their train had derailed, taking the previous two with it. But not only that. Unfortunately, during the derailment, this portion of the train crossed the opposite track. And at that moment, the vehicle headed for Huelva was about to pass through.
The impact was inevitable. The two trains hit each other forcefully, and this in turn caused the derailment of the first two carriages of the second train, which hit an embankment, worsening an already dramatic toll.
Clearly, given the scale of the accident, the railway section was suspended for at least 24 hours, affecting more than 200 trains, but it is very likely that the rescue and train removal operations will require much more time – also considering that the area is not easily reachable by cranes.
But what were the possible causes of this derailment?
The possible causes of the accident in Spain
This train crash is strange – and this is not me saying, but this is what Transport Minister Óscar Puente said. It is strange first of all because the two trains, at the time of the accident, were on a straight stretch. But not only that: a straight stretch that was renovated last May and therefore should not show signs of wear. On this stretch the maximum speed allowed had already been lowered in recent months from 300 km/h to 250 km/h. And one might think that maybe the two trains or one of the two was exceeding the limits…. but in reality no. According to what Álvaro Fernández Heredia, the president of Renfe, declared to a local radio station, the two vehicles were traveling at 205 and 210 km/h respectively. So even from this point of view everything seems to be in order.
So what caused the derailment?
At the moment we don’t know for sure how a train ended up on the opposite track – or, to put it technically, how it managed to occupy the free transit gauge of the adjacent track. In reality, not even the authorities involved in the investigation know this. In a few weeks we will certainly have more detailed information, but the question we can answer is: what could be the causes of a derailment in general, from a technical point of view?
How can a train derail
The causes of the derailment can be grouped into 3 large groups, as also reported by a technical report from ANSFISA, i.e. the National Agency for the Safety of Railways and Road and Motorway Infrastructures.
The first group is the one relating to a broken down al material rolling stockthat is, a failure in one or more mechanical parts of the train. I am referring for example to the suspensions, the undercarriage, the braking system or the wheels. These failures can be linked to wear and tear, poor maintenance or perhaps even design defects.
The second group is the one relating to errors operationalwe could say to human error. In fact, here we are talking, for example, about irregular management of railway exchanges, about wagons being overloaded, or about conditions of excessive speed – which is dangerous, especially when cornering.
The third group is that of faults infrastructural: and this includes any breakages of rails, sleepers, switches, or if these have geometric defects that can reduce contact between the wheel and the rail. Here too the causes are to be found in the wear of the material, in incorrect maintenance or in design defects
To these must be added a fourth group relating to factors externalsuch as obstacles on the tracks, or natural phenomena such as earthquakes, floods or landslides.
And in the case of Spain?
The broken joint hypothesis: what happened
We still don’t know the causes with certainty and this is information to be taken with a pinch of salt, however according to what was stated by the president of Renfethe tragedy could have been caused by – and I quote – “a failure of the rolling stock or infrastructureSo essentially we fall into the first and third categories that we have seen, that is, that of train or railway infrastructure failure.
Do you remember that I told you that last May the network was renovated? Well, this choice was not made by chance: the Madrid-Seville line is in fact the longest running of the high-speed rail network in Spain, having entered service in 1992 with six daily high-speed services managed by Renfe. However, this traffic multiplied with the entry of competitors (such as Iryo) into the state operator, following the liberalization of the market in 2019. So it was not only an old but also a very busy network that needed adjustments.
Nonetheless, Adif, the railway infrastructure manager, has reported 8 accidents over the last few months. We are therefore talking about technical problems that occurred precisely at that point after the renewal of the tracks last May and were mainly linked to the signaling system. The latest report – as reported by the newspaper El Pais – it would only date back to 23 December 2025, when Adif would have reported a fault in the exchanges between Adamuz and Cordoba.
Among other things, it was news from a few hours ago that the authorities – as reported by Reuters – they would have found a broken joint near the point of the accident, and this could have caused a progressive widening of the tracks, to the point of causing the derailment of the last carriage. Even in this case we do not know whether this caused the accident or whether the joint broke due to the derailment. Furthermore, it is “strange” that no train before this one and no periodic inspection has noticed a joint damaged to the point of being close to breaking.
In short, we repeat, it is still early to be sure what happened, but as often happens in these cases it is likely that the cause is not just one but rather a mix of many different ones.
