As workers continued to clear the tracks to restore full service, a smaller number of commuters - many wary and emotional - returned to the rail line, where Mayor Antonio Villaraigosa tried to reassure them the trains are safe.
"I want to dispel any fears about taking the train," he said. "Safety has to be our No. 1 concern, and while accidents can and do happen, taking the train is still one of the safest and fastest options for commuters."
About a dozen bouquets were strung the length of the loading platform at the Simi Valley station as passengers boarded buses and were shuttled to the Chatsworth station, bypassing the tracks still being cleared of wreckage.
Regular commuters said the train load was much lighter than usual.
The National Transportation and Safety Board said the commuter train, which carried 220 people Friday, rolled past stop signals at 42 mph and forced its way onto a track where a Union Pacific freight was barreling toward it. NTSB board member Kitty Higgins said the commuter train engineer, who was among the 25 dead, had failed to stop at the final red signal. The crash also injured 138 people.
The collision occurred at a curve in the track just short of where a 500-foot-long tunnel separates the San Fernando Valley neighborhood of Chatsworth from Simi Valley in Ventura County.
Higgins said investigators will subpoena the cell phone records of engineer Robert Sanchez after two teenage train buffs who befriended him told KCBS-TV that they received a text message from him a minute before the crash.
Investigators did not find a cell phone belonging to Sanchez in the wreckage. The boys' families have been cooperating with investigators, but Higgins declined to characterize their conversations.
"Today we are subpoenaing the phone records of the engineer to determine whether in fact that might have been happening," Higgins told KTTV-TV. Higgins did not return messages from The Associated Press. The NTSB scheduled a 7 p.m. (10 p.m. EDT) news conference.
Jerry Romero, who normally takes Metrolink 111 home but skipped it Friday to pick up a bicycle, said he was disturbed by texting reports.
"That would be pretty disturbing in respect to what we're going through as a society, this fascination we have with gizmos," he said.
In 2003, the NTSB recommended banning the use of cell phones by railroad employees on duty after finding that a coal train engineer's phone use contributed to a May 2002 accident in which two freight trains collided head-on near Clarendon, Texas. The coal train engineer was killed and the conductor and engineer of the other train were critically injured.
The California Legislature last month sent Gov. Arnold Schwarzenegger a bill that would outlaw texting while driving. According to the Governors' Highway Safety Association, four states have banned texting while driving - Alaska, Minnesota, New Jersey and Washington - and similar laws are under consideration in 16 other states.
Metrolink prohibits rail workers from using cell phones on the job.
Audio recordings of contact between Sanchez and conductor on Metrolink 111 show they were regularly communicating verbal safety checks about signals along the track until a period of radio silence as the train passed the final two signals before the wreck. The tapes captured Sanchez confirming a flashing yellow light after pulling out of the Chatsworth station.
The train may have entered a dead zone where the recording was interrupted. Investigators planned to interview the injured conductor about the lapse, Higgins said.
A computer indicated the last signal before the collision displayed a red light, and experts were to test the signals to determine if they worked properly and were in the engineer's line of sight.
"It's really a process of elimination. That's why we're out testing the signals, we're looking at the track, we're examining the equipment, we're looking at what issues that might have been with the engineer and the other crew members," Higgins said.
Investigators will also look at the toxicology report of the engineer, his medical history and his personnel record.
Also Monday, Metrolink spokeswoman Denise Tyrrell resigned after the railroad's board said her Saturday announcement that the engineer's mistake likely caused the crash was "premature."
Passenger Art Reis expressed concern as he rode the train to work that authorities might not be completely candid with the public after the investigation is done. He said he was concerned that Tyrrell resigned almost immediately after announcing that the agency was responsible for the crash.
"It's all image and politics, and that's what concerns me," said Reis, 70.
Metrolink did not immediately return phone messages seeking comment.
Associated Press writers Jeff Wilson, Christina Hoag and John Rogers contributed to this report.