(AP) SAN FRANCISCO - Two investigators from the National Transportation Safety Board were helping San Francisco officials on Sunday determine the cause of a collision between two light-rail trains that left dozens of people injured.
The investigators will work with transit officials to interview the train drivers, passengers and witnesses, said NTSB spokesman Peter Knudson.
The NTSB will also focus on assessing the condition of the train tracks, signal systems and the structural integrity of the train cars involved, Knudson said.
A chaotic scene on Saturday unfolded after a westbound L train struck a K train that was sitting at a boarding platform in the West Portal Station. In all, 48 people were taken to area hospitals with minor to serious injuries.
A train operator was among the four people hospitalized with more serious injuries, but officials on Sunday said none of the injuries were considered life threatening.
Rescue crews found the wounded operator pinned inside his damaged compartment, said San Francisco Fire Lt. Ken Smith.
"He was in the front of the train, and part of it was pushed into him," Smith said. "Rescuers had to pry open the doors to get to him and assist him out of the light rail vehicle."
Smith said the driver told recuers he was having pains in the abdominal area.
In all, 15 ambulances and seven fire engines responded to the scene, Smith said. It took about 90 minutes to evacuate all 48 people, some bloodied and with broken noses, bruises and other injuries, to two hospitals.
A day after the crash, cafes and shops in the western San Francisco neighbourhood shopping district were still buzzing.
Ercan Bektas, 27, a waiter at the Squat and Gobble Cafe and Crepery, located at the intersection where the crash occurred, said he was startled by the sound.
"I was about to punch out, and heard something like a bomb," he said. Bektas said he ran outside to help people before rescue crews arrived.
"There was smoke coming out of one car. I went to help and I saw the car crushed," he said.
After the crash, witnesses said injured passengers, some with bloody wounds, sat on the station's boarding platform.
The most seriously injured were treated by rescue workers at a triage centre, then taken on stretchers to waiting vehicles and whisked to hospitals.
Associated Press Writer Tim Reiterman contributed to this report.