WASHINGTON, June 23, 2009 -- Investigators in northeast Washington, D.C., Tuesday at the site of the deadliest accident in Metro history began examining why systems designed to keep trains safe failed Monday evening at the height of rush hour.
With nine people dead and 76 sent to area hospitals -- some of whom are critically injured -- the accident site remained a rescue scene Tuesday, with a crane and cadaver dogs brought in to find people who were possibly still trapped on the trains.
Watch "World News With Charles Gibson" tonight at 6:30 ET for the full report.
Today investigators said the two trains that collided were likely being run by computers that control speed and braking. Officials said Metro trains travel above sensors along the rail that can automatically detect when trains are getting too close to one another. The computerized systems stops them from coming within 1,200 feet of each other, and investigators need to find out why it didn't work.
"What causes us concern the most is the fact that this was not supposed to happen," said Jackie Jeter, president of Amalgamated Transit Union Local 689 today. "There are safety mechanisms that are on place on the trains to prevent this type of accident. And, for me, as president of the union and as a train operator, I have to wonder why didn't those safety mechanisms kick in and prevent it."
It's still not clear whether the crash was the result of an operator error, a train malfunction, or a problem in the computer system.
"It's much too early to speculate as to what actually happened," former National Transportation Safety Board investigator Barry Sweedler said, adding that investigators will take a close look at the automatic train controls.
Sweedler also said train recorders will provide insight into what happened as the information is evaluated over the next few days. The train that was hit had several recorders on it, but the one that collided into it didn't have any.
NTSB Had Warned Metro Trains Could Be Dangerous
No matter what caused the accident, passengers traveling in the approaching train were in an older car that did not protect them as well as it should have.
In 1996, a Metro train of the same series failed to stop and crashed into an unoccupied train in what the NTSB called "catastrophic failure." After the crash the NTSB recommended a comprehensive evaluation of the cars. In 2002, D.C. Metro declined to make any changes. A similar crash took place in 2004, and the NTSB reiterated its warnings.
"In 2006 [the NTSB] asked them to look at old cars," Deborah Hersman, the NTSB investigator for Monday's crash, told "GMA" today. "They did not retrofit the cars to the standard the safety board was looking for."
Hersman emphasized that the NTSB's role was to make recommendations, and that it was up to local and federal authorities to decide whether to act based on those recommendations.
"The Safety Board is in the business of investigating accidents and making recommendations," Hersman said. "The safety board is going to be looking very closely to what has been done."
"This is the first crash of a Metro train where there are a large number of fatalities, so these crashes are very, very few and far between," Sweedler said. "But that doesn't mean that the greatest and best technology shouldn't be used to protect passengers when these rare events do occur."
"The NTSB is looking at operations, we're looking at maintenance, we're looking at the tracks," Hersman said. "We'll be looking at performance of the equipment as well as survival factors."
Homeland Security Department spokeswoman Amy Kudwa told The Associated Press that federal authorities had no indication of any terrorism connection at this point in the investigation.
Passengers Recount Deadliest Crash in Metro History
The accident happened when a stopped Metro train, waiting for clearance into the Fort Totten station, was struck from behind by a second train, according to D.C. fire officials. It occurred at 4:59 p.m. on the city's red line in northeast Washington between the Takoma Park and Fort Totten stations.
A D.C. alert Monday evening said, "Metro reports that two trains collided and one train is on top of the other train."
From his seat in the second car of his train, passenger Brad Sander said, "We saw the first car go up in the air."
"I slid off my seat, and just fell on the floor, not injured, and we found the emergency exit, and jumped out, and I called 911, and tried to just attend to the injured," Sander told ABC News today.
Passenger Father Dave Bottoms could only watch as the train car he sat in plowed into a stopped train ahead, crumpling its frame and sending a "wave" of wreckage toward him.
"I began praying," Bottoms told "Good Morning America" today. "It slowed down about three seats in front of our area."
Bottoms said that when the screeching of the metal stopped, the screaming started -- a woman and a man in his car had been pinned under some collapsed seats.
"A few people released themselves and climbed over the wreckage," Bottoms said. "I heard her screaming. I talked to her, encouraged her."
Bottoms said he assured the woman that they were not going to leave her and then led the rest of the passengers in the Lord's prayer. After a passenger busted out a window with a fire extinguisher, a police officer climbed in and directed the passengers as they lifted the seats off the trapped woman.
Bottoms didn't see whether the woman got all the way out, but "her pulse was strong," he said. "She was quiet."
The woman was likely one of scores taken to hospitals following the horrific crash that D.C. officials called the deadliest in the Metro's history.
One of the victims is a female Metro employee, identified as Jeanice McMillan of Springfield, Va., by Metro spokesman Steve Taubenkibel. McMillan was driving the rear train. She had been running Metro trains only since December. Investigators plan to subpoena her cell phone records to see if she was distracted on the phone or texting at the time of the accident.
According to D.C. fire chief Dennis Rubin, the injured were taken to various hospitals, including Howard University Hospital and Washington Hospital Center. At least 50 were walking wounded, around 14 suffered non-life-threatening injuries, and six suffered critical injuries, he said.
Dr. Johnnie Ford, a Howard University Hospital emergency room physician, told the AP that a 14-year-old girl suffered two broken legs in the accident.
Washington, D.C., Police Chief Cathy Lanier advised family members of passengers to call (202) 727-9099 for more information. A secondary number issued by local district officials is (202) 737-4404.
Other Train Accidents
Past accidents on Washington's Metro have included a January 2007 train derailment near the Mt. Vernon Square Station on the green line, in which 23 passengers were transported to local hospitals for treatment and released; a November 2006 accident where a train struck and killed workers in Alexandria, Va.; and a May 2006 accident where a train struck and killed a worker near the Dupont Circle Station.
In November 2004, two trains collided at the Woodley Park-Zoo/Adams Morgan Station, and about 20 people were taken to nearby hospitals.
Elsewhere, a train derailed in Rockford, Ill. earlier this month, prompting the train cars holding flammable ethanol to explode.
Last year, 25 people died in Southern California when a Metrolink commuter train and a freight train collided. The Metrolink train engineer, who died in the head-on collision, was sending text messages just before the accident.
ABC News' Devin Dwyer, Jason Ryan, Jack Date, Bret Hovell, Matt Hosford and The Associated Press contributed to this report.