Federal officials blamed railroads Monday for refusing their requests to install an expensive safety feature on all U.S. tracks that many say could have prevented Southern California's deadly commuter train crash.
Railroads have balked at the cost and reliability of the technology, which is in use on only 2,600 miles of track out of about 140,000 miles nationwide.
The technology has not been installed on the Los Angeles track where 25 people died in a crash on Friday.
"Many times in this country, we regulate by counting tombstones," said Barry M. Sweedler, former director of the Office of Safety Recommendations for the National Transportation Safety Board.
"Unfortunately, it takes a tragedy like this with many people dead for action to take place, even though people in the know knew what needed to be done and didn't do it," he said.
The system known as positive train control monitors train location and speed using satellite-based positioning systems and digital communication. It can engage the brakes if a train fails to heed signals or gets on the wrong track.
The head-on collision between a Metrolink commuter train and a Union Pacific freight train was the deadliest rail accident in 15 years. The commuter train drove through three warning light signals before striking the freight train.
NTSB board member Kitty Higgins has said the positive control technology could have prevented the crash.
"I've seen it tested," she said. "It makes a difference."
Rep. Jim Oberstar, chairman of the House Transportation Committee, said in statement the accident was preventable and "the unwillingness of rail companies to make the needed investments in safety have prevented this technology from being fully implemented."
The Association of American Railroads, the lobbying arm for the freight railroads, said it has concerns that the technology has not been perfected.
"This is not off-the-shelf technology. You can't put something like this into place unless it's been thoroughly tested and proven to be effective," association spokesman Tom White said.
Congress has approved different versions of a bill that would require major railroads to develop a plan to use positive train control, but final legislation has not been passed.
The Federal Railroad Administration said it would cost at least $2 billion to install the technology nationwide. The railroads would likely carry the bulk of that cost.
Part of the challenge, officials said, is getting the nation's railroads to install systems that are compatible.
It could take five years to resolve technical issues, even before the system goes into widespread use, the Federal Railroad Administration said.
In Massachusetts, the commuter rail system is equipped with sensor technology designed to stop a train on the tracks if it fails to stop at a signal or if another train is in its path.
The system, known as "Cab Signal with Positive Stop," was used in March, when a 112-ton freight car parked at a lumber yard came loose and barreled almost three miles along the tracks toward a commuter rail train carrying 300 passengers during rush hour. The technology sensed the freight train on the tracks and stopped the commuter train.
The freight train still struck the commuter train, and 150 people suffered mostly minor injuries. But the impact was not as severe as it could have been, said Joe Pesaturo, a spokesman for the Massachusetts Bay Transportation Authority.
Train accidents in the U.S. have remained fairly constant over the past decade. A total of 2,617 accidents, which include collisions and derailments, were reported last year.
Metrolink dispatchers use computers to monitor train traffic and send signals to control flow along the tracks. Engineers are required to obey trackside signals, which are then relayed by radio to a conductor on board. Those conversations can be heard by the dispatcher and are recorded.
It remains unclear what, if anything, was said between the engineer and conductor before the crash in Los Angeles. A dispatcher tried to alert the Metrolink engineer about the oncoming train, but the call came too late.
A spokesman for Metrolink, which carries about 50,000 riders a day, did not respond to an e-mail seeking comment.
Experts say a safety system that relies on track signals is open to tragic mistakes.
"The red light is the last straw," said University of Southern California engineering professor Najmedin Meshkati. "The light bulb could go out and you would not have a red signal."
The Los Angeles collision was the deadliest passenger train crash since Sept. 22, 1993, when Amtrak's Sunset Limited plunged off a trestle into a bayou near Mobile, Ala., moments after the trestle was damaged by a towboat; 47 people were killed.