Investigators face a daunting challenge to sort out the bizarre half-mile journey of an out-of-service, possibly driverless CTA "ghost train" that breached multiple safeguards before colliding with another Blue Line train Monday morning.
The accident that sent more than 30 people to hospitals was unlike any that veteran city rail workers say they have seen: A train maneuvers around the curves in the Forest Park rail yard, passes through at least two track switches — any one of which should have stopped the train — continues past the station platform, then climbs up and over a small hill near the Eisenhower Expressway before accelerating to about 20 mph and ramming the stopped train at the Harlem stop shortly before 8 a.m.
"The million-dollar question is, 'How did this happen?'" said Robert Kelly, president of the CTA rail workers union. "This is baffling everybody."
The head-on impact occurred with 40 people aboard the standing train. Most of those hurt reported only light injuries after the crash, during which the front ends of both head cars puckered to absorb the force of the crash and protect occupants, as they are designed to do. The seats in the impact area were still intact.
The unanswered questions are the subject of an investigation being led by the National Transportation Safety Board. As a precaution, the Federal Joint Terrorism Task Force is also involved in the investigation, a law enforcement official said.
The probe stems from the fact that numerous redundancies are designed to prevent any single break in the safety chain from leading to an accident.
If the train were properly parked in the yard, the friction brakes would be applied to prevent the rail cars from moving, regardless of whether electrical power was being delivered to the train, CTA officials and rail workers told the Tribune.
A universal key that opens the cab doors on all CTA trains would be needed to enter the cab compartment, and a separate key would be needed to turn on the master controller and release the brakes, according to CTA operators.
In addition, to prevent a runaway train, CTA rail cars are equipped with a "dead man control." The train operator must turn the handle of the master controller and keep his or her hand on the handle to release the brakes and deactivate the dead man switch. If the handle is released while the train is moving, the motor automatically shuts off and the brakes are applied, officials said.
Further, the cab signal system aboard CTA trains makes a beeping sound that is familiar to passengers when a train is exceeding the speed limit. The cab signal gives the operator about 2 seconds to reduce speed before it automatically applies the brakes.
A red light in the cab would have also come on, because after the four-car train left the yard it was on the wrong tracks for an inbound train to Chicago, leading to its head-on collision with the outbound train to the Forest Park terminal, officials said.
A source close to the investigation said it will be important to learn what the trackside signals showed at the time of the accident. At the track switches, called interlocks, trip devices are supposed to be engaged to put the train into emergency braking mode if it doesn't have the proper lineup.
Investigators will determine whether the fail-safe trip mechanisms failed and if the switches were properly aligned, CTA spokesman Brian Steele said.
Investigators will also focus on scenarios such as the possibility that CTA rail yard personnel did not do their job properly or that fail-safe equipment malfunctioned.
Nothing so far has pointed to a mechanical failure or a crime, but neither has been ruled out, Steele said.
The NTSB investigation includes a team of experts who will study the signals, mechanical systems, operations and the possibility of human error, said Tim DePaepe, the safety board's investigator in charge.
"We don't jump to conclusions," DePaepe said during a news conference at the accident scene. "I've heard five different scenarios on my drive over here. I can't believe all five are right, because they can't be."
Unlike on commercial airplanes, there are no "black boxes" on CTA trains that record accident data. But surveillance cameras on the trains, in the stations and at the yard will help tell the story of what transpired over a matter of just a couple of minutes, Steele said.
A preliminary review of some video shows that no operator was at the controls of the out-of-service train, he said. There also were no signs of forced entry or vandalism to the train, he said.
But that review does not thus far indicate whether someone was in another part of the head car or in the other three cars attached to it, Steele said.
A CTA supervisor at the Forest Park station and a motorman aboard a train said they saw no one on the train leaving the yard, said Kelly, Local 308 president
of the Amalgamated Transit Union.
Such early indications that no one was driving prompted some longtime CTA employees to dub it a "ghost train."
Tribune reporters Wes Venteicher and Hal Dardick contributed.