At least 69 people were killed and more than 100 were injured when two high-speed trains collided near Urda, south of Madrid.

The two trains crashed into each other.

He said the control center then allowed trains to move again without speed limits.

The place where staff manage train movements.

They also need to establish what information the control center had about the stopped train.

The place where staff manage train movements.

The minister’s account points to the control center’s decisions.

The place where staff manage train movements.

This is called driving by sight.

Drivers use what they can see ahead to decide how to drive.

When it failed, a backup system called Lateral Signalling Block was used.

A system used as a substitute when the main system fails.

Lateral Signalling Block is a backup system used when automatic signals or data transmission fail.

A system used as a substitute when the main system fails.

They also need to establish what information the control center had about the stopped train.

To find out or confirm something with certainty.

Investigators are examining why the safeguards did not prevent the collision.

Safety measures designed to protect people or prevent an accident.