LOS ANGELES — Investigators on Tuesday were conducting a test to determine when the engineers of two trains were able to see each other in the moments before the head-on crash that killed 25 people.
The visibility test involving stand-in engines is part of the ongoing investigation into the crash that the Metrolink commuter rail service has blamed on the failure of its engineer to stop for a red signal.
Just before Friday’s collision in the Chatsworth section of Los Angeles, a Union Pacific freight train had emerged from a tunnel and the commuter train was rounding a horseshoe bend.
‘‘When did one come into view with the other?’’ Kitty Higgins, a board member of the National Transportation Safety Board, said before the test. ‘‘What will that tell us?’’
NTSB officials said it would be the final test conducted at the crash site. Officials hoped to open the newly repaired tracks to freight and commuter service later in the day Tuesday.
It was the deadliest rail disaster in the U.S. in 15 years.
Tuesday’s test at the wreck site was watched by Lilly Varghese, a friend of 57-year-old victim Beverly Mosley.
‘‘I came here to pay respect to where I lost her,’’ Varghese said. ‘‘She lost her soul here.’’
Varghese said she and Mosley worked together as nurses in the prenatal unit of a hospital. Mosley had two adult daughters and had become a grandmother about seven months ago.
In Washington, Sen. Dianne Feinstein introduced legislation Tuesday requiring the installation of technology to prevent train crashes and warned that there would be more disasters without it.
The California Democrat hopes to nudge Congress to pass her requirement for so-called positive train control before recessing at the end of next week. The House and Senate have already passed separate legislation to implement the technology but time is running out to reconcile the differing versions.
The technology can engage the brakes if a train misses a signal or gets off track. It has been installed on a fraction of U.S. rail tracks but not on the one where Friday’s crash occurred.
Feinstein blamed ‘‘a resistance in the railroad community in America’’ to the price tag of installing the systems.
Failure to act now, she said, amounts to ‘‘negligence, and I’ll even go as far to say I believe it’s criminal negligence not to do so.’’
The Association of American Railroads, the lobbying arm for the freight railroads, has said it does not oppose the legislation but is concerned that the technology has not been perfected.
Meanwhile, federal investigators were continuing to look into whether the engineer of the Metrolink commuter train was text messaging on a cell phone before Friday’s deadly wreck. The engineer, Robert Sanchez, was killed in the collision.
Investigators with the NTSB did not find a cell phone belonging to 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.
NTSB board member Kitty Higgins said her agency issued a subpoena to get the engineer’s cell phone records. She said Verizon Wireless had five days to respond to the demand.
Higgins also said tests at the crash site showed the red and yellow signals were 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?’’
Jerry Romero, who normally takes Metrolink 111 home but skipped it Friday to pick up a bicycle, said he was upset 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.
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.
The commission is scheduled to vote on the order Thursday.
Metrolink prohibits rail workers from using cell phones on the job, but federal regulations do not address the issue, Federal Railroad Administration spokesman Steven Kulm said.
In 2003, the NTSB recommended that the FRA 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 in Texas. The coal train engineer was killed and the conductor and engineer of the other train were critically injured.
Associated Press writers Erica Werner in Washington and Jeff Wilson, Christina Hoag and John Rogers in Los Angeles contributed to this report.