LOS ANGELES — Amid a federal investigation into whether a commuter train engineer was texting before a deadly collision with another train, the state’s top rail safety regulator is seeking an emergency order banning train operators from using cell phones.

“Some railroad operators may have policies prohibiting the personal use of such devices, but they’re widely ignored,” Michael Peevey, president of the California Public Utilities Commission, said Monday. “Our order would make it the law and we’ll go after violators. We owe it to the public.”

The commission has scheduled a vote on the order Thursday.

The collision between the Metrolink train and a Union Pacific freight train killed 25 people and injured 138 people — the deadliest rail disaster in the U.S. in 15 years.

Metrolink has blamed its engineer for not heeding a red light signal designed to prevent such wrecks, and the National Transportation Safety Board is reviewing whether the engineer was text messaging.

Investigators did not find a cell phone belonging to Robert Sanchez in the wreckage, but two teenage train buffs who befriended him told KCBS-TV that they received a text message from him a minute before the crash.

Kitty Higgins, an NTSB board member, said her agency issued a subpoena Monday to get the engineer’s cell phone records. She said Verizon Wireless has five days to respond to the subpoena request.

Higgins also said tests at the crash site showed the signals are working properly and there were no obstructions that may have prevented the engineer from seeing the red light.

“The question is, did he see it as red?” Higgins said. “Did he see it as something else? Did he see it at all?”

NTSB experts prepared to conduct a simulated crash test on Tuesday.

On Monday some commuters — many wary and emotional — returned to the rail line on the first day of service since the accident. Regular commuters said the train load was much lighter than usual.

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.”

The NTSB said the commuter train, which carried 220 people, rolled past stop signals at 42 mph and forced its way onto a track where a Union Pacific freight was barreling toward it.

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.

About a dozen bouquets were strung the length of the loading platform at the Simi Valley station as passengers Monday boarded buses and were shuttled to the Chatsworth station, bypassing the tracks still being cleared of wreckage.

Commuters will use the buses again Tuesday morning.

Jerry Romero, who normally takes a Metrolink train home but skipped it Friday to pick up a bicycle, said he was disturbed by reports that the engineer may have been texting.

“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 that the Federal Railroad Administration regulate 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.

Metrolink prohibits rail workers from using cell phones on the job, but there is no existing federal regulation regarding the use of cell phones by railroad employees on the job, FRA spokesman Steven Kulm said.

Audio recordings of contact between Sanchez and the conductor on the Metrolink 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 before pulling out of the Chatsworth station.

The train may have entered a dead zone where the recording was interrupted. Investigators tried to interview the conductor about the lapse Monday, but he declined because a company representative was not able to be present, Higgins said. He is still hospitalized with serious injuries.

A computer indicated the last signal before the collision displayed a red light, and experts tested the signals Monday and determined they were working properly.

On Tuesday they planned to take actual Metrolink and Union Pacific trains to recreate the events leading up to the accident and to test the signals further.