What caused Spain's deadly train crash that killed 69?

A malfunctioning railway safety system, a controversial decision by a traffic controller and mounting pressure on Spain's high-speed rail network have emerged as key factors under scrutiny after a devastating train collision killed 69 people.

The crash near the village of Urda in central Spain on Wednesday was the country's second major rail disaster this year. It has raised serious questions about the safety of a network long regarded as one of Spain's greatest infrastructure achievements.

Transport Minister Óscar Puente has blamed an erroneous instruction from a railway controller that allowed one train to resume travelling at normal speed despite another train remaining stationary ahead.

But railway unions reject attempts to place responsibility on an individual worker. They say ageing safety equipment, understaffing and increased workloads have created conditions in which mistakes can have catastrophic consequences.

A judge and a special government commission are investigating the disaster.

How did the crash happen?

According to a timeline released by the Spanish government, the chain of events began at 8.30am on Wednesday when a computer malfunction disrupted the railway's LZB safety system.

The system monitors the position of trains and can automatically trigger braking to prevent collisions.

When it stopped working, trains on a 63km section of the Madrid-Seville line came to a halt. Human controllers operating from Madrid assumed responsibility for monitoring train movements along the affected stretch.

Authorities believe six trains were on that section of track at the time.

At 8.36am, a controller instructed a train operated by state-owned RENFE to resume travelling at normal speed.

Another train, operated by privately owned IRYO, was stationary about 25km further down the line. Its driver had been unable to override the automatic stop and had informed the controller.

At 8.53am, the RENFE train collided with the stationary IRYO train from behind.

The impact derailed carriages and scattered wreckage down a gravel slope near Urda.

At least 69 people were killed, while 50 remained hospitalised on Thursday, according to regional authorities.

Why is the government blaming human error?

Transport Minister Puente described the controller's decision as "inexplicable" and "erroneous."

He said the RENFE train should never have been allowed to resume normal operation because a stop signal remained active on the line.

"An order is given for the train to restart, an erroneous decision," Puente told reporters.

The decision "was taken in inexplicable circumstances given that a train was stopped and with a red light," he added.

According to the minister, the train should either have remained stationary or, at the very least, received instructions to proceed at reduced speed.

The government therefore considers the decision to restart the train without speed restrictions a critical factor in the collision.

What went wrong with the safety system?

The malfunction involved LZB, a train protection system used on the Madrid-Seville high-speed line.

Normally, the technology monitors trains and can intervene automatically to prevent a collision. Its failure left controllers responsible for ensuring safe movements along the affected section.

Railway unions say the system is ageing and has experienced repeated problems.

"The LZB system should have been replaced some time ago," said Diego Martín, spokesperson for SEMAF, Spain's train engineers' union.

"It failed us yesterday (Wednesday) and it has gone offline on repeated occasions in the past."

The system has been in use for around three decades and is being phased out.

Investigators must now establish why it failed and whether existing backup procedures were adequate.

Why are railway unions challenging the government?

Unions argue that focusing exclusively on the controller's decision ignores the working conditions under which railway staff operate.

They say traffic controllers have repeatedly requested more personnel while dealing with growing workloads and recurring technical failures.

Raquel Ayllón, spokesperson for the SCF railway traffic controllers' union, criticised the minister's explanation.

"We believe (the minister) is blaming a mere worker who was working under increasingly poor conditions," she told The Associated Press.

"Human error isn't incomprehensible. What is incomprehensible is that the safety system is regularly failing."

Pepa Páez of the CCOO union also called for investigators to examine the broader system rather than concentrate solely on an individual mistake.

"The focus should not be on if there was a human error, but rather what is wrong with the system, what situations must be improved so that if there is a human error we don't find ourselves in this situation," she said.

Rail workers held a previously planned strike on Thursday to demand safety improvements promised after an earlier deadly collision in January.

Has increased rail traffic contributed to the problem?

Spain opened its high-speed rail network to private competition in 2021, allowing operators to compete with state-owned RENFE.

The change increased the number of services on some routes.

According to the SCF union, average daily train journeys between Madrid and Barcelona rose from 56 in 2019 to 89 in 2024.

Railway workers argue that the expansion has increased pressure on infrastructure and traffic controllers.

Joan Rodríguez, a spokesperson for Spain's train workers' union, questioned whether investment in maintenance had kept pace with the growth.

"We are not convinced that the liberalisation of the high-speed passenger rail service was matched by the necessary upkeep of the lines," he told Spanish broadcaster TVE.

"I am not saying it was a determining factor (in the crashes), but yes, the increase in use of the network is a factor to keep in mind."

Investigators have not established whether increased traffic contributed to Wednesday's collision.

Why is the crash particularly alarming?

The disaster comes just nine months after another deadly collision on the same Madrid-Seville rail corridor.

In January, one train derailed and struck another travelling in the opposite direction, killing 46 people.

Both incidents involved trains operated by RENFE and IRYO.

Spain's high-speed rail network, launched in 1992, is the world's second-largest after China's and had previously enjoyed a strong safety reputation.

The two disasters have now killed 115 people in a single year, dealing a severe blow to public confidence.

Prime Minister Pedro Sánchez has promised to investigate the latest crash and strengthen railway safety.

"It is not acceptable for a country like Spain to endure two high-speed train accidents in the same year," he said.

King Felipe VI also demanded answers after visiting injured passengers at a Toledo hospital.

"This investigation must determine how and why this catastrophe happened," he said. "We will have to take measures so this never happens again."

What happens next?

The judicial investigation and a separate government inquiry will examine the safety system failure, the controller's instructions and the circumstances that allowed two trains to collide.

They will also face questions about whether staffing levels, operating procedures and infrastructure maintenance provided sufficient protection when automatic safety systems failed.

For now, the crucial question remains unanswered: Was the disaster primarily the result of one controller's mistake, or did deeper weaknesses in Spain's railway system turn a technical malfunction into a catastrophe?

- with inputs from AP