According to the L.A. Times, federal investigators found that the red light was not as bright as other lights along the track.
The conductor, who was also text-messaging seconds before the crash, ran the light before colliding with the freight train. He was killed in the crash.
Metrolink is already planning to install more visible signal bulbs.
The dimmer red light was preceeded by two yellow lights that warned of the upcoming stop.
The Associated Press contributed to this story.
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