Ric Francis, Associated Press
Officials walk Monday near site where a commuter train smashed into a freight train Friday in Chatsworth, killing 25. Investigators want to determine if the Metrolink engineer was text messaging.

LOS ANGELES — Federal officials said Monday that it could take five years or more to put an early warning system in place across the country to prevent the kind of rail collision here Friday that killed 25 people and left more than 130 injured.

The accident, a head-on rush-hour collision between a Union Pacific freight train and a Metrolink commuter train in the San Fernando Valley, has revived demands for "positive train control."

That is a catch-all term for systems that use satellites, transponders and other devices to track trains and automatically stop them if they ignore red lights or encounter other trouble.

Those systems are in limited use on 240 miles of track, including high-speed sections of Amtrak's Northeast Corridor, and are undergoing tests on an additional 2,600 miles of track in 16 states.

Legislation is pending in Congress that would require large railroads to develop the systems by 2014.

Federal investigators say the signal light worked normally and there were no obstructions that would have prevented the engineer from seeing the red light.

The National Transportation and Safety Board also said Monday night it has requested cell phone records to investigate whether the Metrolink engineer was text messaging before his commuter train collided with the freight train.

The agency says the Metrolink train rolled past stop signals at 42 mph and forced its way onto a track with a Union Pacific freight.

The Metrolink engineer, Robert Sanchez, was among 25 people who died.

On Saturday, Denise Tyrrell, a spokeswoman for Metrolink, said the crash had probably been caused by the failure of Sanchez, to heed a red signal.

Tyrrell resigned Monday after the Metrolink chairman, Ron Roberts, issued a statement saying her assessment had been premature.

On Monday, the first workday since the crash, Metrolink reported a nearly 40 percent decline in ridership on trains headed toward Los Angeles from Ventura County, the line where the accident occurred. With Los Angeles freeway traffic clogged as always, Mayor Antonio R. Villaraigosa took a trip on Metrolink to urge commuters not to give up on the service.

"I want to dispel any fears about taking the train," Villaraigosa told reporters.