Authorities in Los Angeles fear possible copycat attempts by people trying to commit suicide after a depressed man parked his car across rail lines on Wednesday in an apparent suicide bid.
The California man could face the death penalty for triggering the crash that killed 11 people in Los Angeles.
Police said Wednesday's crash was caused by Mr Juan Manuel Alvarez (25) when he slashed his wrists and stabbed himself in the chest shortly before parking his sport-utility vehicle on rail tracks. Mr Alvarez has a history of mental, family and drug problems.
He jumped clear at the last moment but one commuter train hit his car and derailed into the path of another. Almost 200 people were injured in the collision north of Los Angeles.
Los Angeles County District Attorney Steve Cooley said 11 counts of murder had been filed against Mr Alvarez, including a "special circumstances" allegation that meant prosecutors could decide to seek the death penalty if he is convicted.
Mr Alvarez was not injured in Wednesday's crash and was under suicide watch in the jail ward of a local hospital.
In what they described as a similar incident, police said they had arrested another man (25) who parked his car at dawn diagonally across rail tracks in Irvine, 30 miles south of Los Angeles, with the intention of killing himself.
Police were alerted and approached the driver, who pulled away and led officers on a car chase before being persuaded to get out of his vehicle.
Police said the man, named told them he had planned on committing suicide by being struck by a train. He is being held in jail pending mental-health investigations.