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Mark J. Terrill, File, Associated Press
In this Tuesday, Feb. 24, 2015, file photo, Workers stand near a Metrolink train that hit a truck and then derailed in Oxnard, Calif. Three cars of the Metrolink train tumbled onto their sides, injuring dozens of people in the town 65 miles northwest of Los Angeles. Engineers have figured how to blunt the deadly force of a train smashing into a truck on the tracks. Yet few U.S. rail systems have adopted the technology, which is believed to have played a significant role in the remarkably low number of serious injuries from Tuesday's commuter rail crash in California.

LOS ANGELES — Technology that can blunt the tremendous force of a head-on collision appears to have paid off in the remarkably low number of serious injuries suffered when a Southern California commuter train slammed into a truck abandoned on the tracks.

And yet very few commuter train systems in the U.S. have this "crash energy management" technology.

Metrolink began investing heavily in new passenger cars with the technology after a 2005 crash that killed 11 people. Three of the four cars in Tuesday's accident had the new design, which disperses the energy of a crash away from where the passengers sit.

For years, federal regulators have weighed rules that might require such technology. But they have not formally proposed such measures.