Schiavi said the train was recorded slowing from about 30 miles per hour (50 kph) to 12 miles per hour about 40 yards (meters) before the impact. "We don't know what happened in those final 40 meters," he said.
The train slammed into a shock-absorbing barrier at 8:33 a.m., smashing the front of the engine and crunching the much lighter cars behind it. The second car penetrated nearly 20 feet (six meters) into the next, Schiavi said.
Most damaged was the first car, where passengers shared space with bicycles. Survivors said many people were injured in a jumble of metal and glass. Security camera images showed windows exploding as the cars crumpled into each other like an accordion, with a man on the adjacent platform scrambling across the tracks to escape the wreck.
It was Argentina's deadliest train accident since Feb. 1, 1970, when a train smashed into another at full speed in suburban Buenos Aires, killing 200.
President Cristina Fernandez canceled her day's agenda due to the accident, which raised fresh doubts about government investment in the train system millions depend on. While largely privatized, the system depends on huge state subsidies, and fares are relatively low compared to other countries in the region.
Union leaders blamed what they called a history of failure to invest in maintaining or replacing aging trains.
The Trains of Buenos Aires company promotes its low fares on its website, saying that passengers pay just 23 cents a ride on average, compared to 80 cents in Santiago, Chile, and $1.11 in Sao Paulo. But TBA also complains that without higher fares, maintenance is a struggle.
Employee salaries and benefits have soared nearly 900 percent in the last decade, while the TBA now spends just 12 percent of its operating costs on maintenance, the company said.
Railway experts told The Associated Press that accidents like this are common among older trains that lack modern designs. The TBA has bought many cast-offs from other countries that have modernized their systems, and uses hundreds of Japanese-made "Toshiba Classic" rail cars that were built in the 1960s.
"That's a very slow speed" for so many casualties, said University of Southern California engineering professor Naj Meshkati, who studies rail disasters. "It's important to look at the age of the cars."
Trains using older cars can lesson the danger by running an empty and locked "deadhead" car between the engine and the passenger cars, said Colin Fulk, a rail expert and consultant in Sherrills Ford, N.C. Argentina's commuter trains don't do this.
The TBA said it is cooperating in the investigation.
"This is not an accident whose causes will be hidden from view in any way," Schiavi promised, noting that recorders, security cameras, computer systems and other evidence would be handed to investigators.
There have been a half-dozen serious train accidents in Argentina in the last 15 months. Last September, a bus driver crossed the tracks in front of an oncoming train, killing 11 people. Two months later, a bus driver transporting children on a field trip drove in front of a train, killing eight schoolgirls.
Debora Rey in Buenos Aires and Martha Mendoza in Santa Cruz, Calif., contributed to this report.
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