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. 
 
 jhilkevitch@tribune.com 
 
 Twitter @jhilkevitch ||||| UPDATED: 10/1/2013 5:30 a.m. 
 
 CHICAGO (CBS) — Authorities are trying to determine what caused two CTA Blue Line trains — one of them apparently without an operator — to collide Monday morning and injure dozens of rush-hour passengers. 
 
 A westbound train with about 40 passengers was standing on the tracks near Harlem Avenue in Forest Park when an eastbound train — without a controller — traveling on the same track smashed into it. 
 
 Police were investigating the possibility that somebody deliberately caused the accident. However, CTA and federal officials believe the crash was likely an accident. The National Transportation Safety Board was in charge of the investigation. 
 
 On Tuesday morning, the trains remained at the Harlem station, which is closed for the morning rush hour. The Blue Line will stop at all other stations, while the NTSB continues its investigation. 
 
 Suspicion that the train was stolen or hijacked was raised because the train that caused the crash only had four cars. Rush hour trains typically have many more cars and would not have left the train yard with so few cars. 
 
 The CTA has confirmed that the eastbound train was on the wrong tracks. 
 
 Forest Park Mayor Anthony Calderone told CBS 2’s Mike Puccinelli that nobody was at the controls of the train when it crashed around 8 a.m. 
 
 Police are treating the accident as a crime scene. Later Monday, white canvas panels concealed the spot where the two trains had collided. 
 
 Brian Steele with CTA says there is no indication of criminal activity. The CTA is working under the theory that the accident was due some sort of mechanical malfunction. 
 
 The train that hit the standing train had been marked “out of service,” said Steele, who said the collision occurred at a “pretty slow speed.” 
 
 Federal officials say on background that all indications are that the crash was an accident. 
 
 Robert Kelly, of Amalgamated Transit Union 308, said somebody would need a key to fire up and then drive the train from the Forest Park train yard, where one end of the Blue Line originates. 
 
 “The million dollar question is, how did this happen?” Kelly said. 
 
 Kelly said surveillance cameras that could have recorded the rogue train’s departure were not working. 
 
 At least 33 people were hurt when the trains collided in west suburban Forest park, according to the CTA. All of those injuries were on the standing westbound train. There were a total of about 40 people on that train. 
 
 “We were standing still and then all of a sudden something hit us and I got shot forward into the front seat,” said one passenger as she limped to a responding ambulance. 
 
 Kelly told CBS 2 the train may have been traveling upwards of 20 to 25 miles per hour when it hit the stationary train, and its unclear if there was a motorman on the moving train when the collision happened. 
 
 None of the injuries was believed to be life-threatening. 
 
 One of the many questions: How did the eastbound train manage to leave the Forest Park rail yard and pass over at least two interlocking systems that should have triggered the brakes? 
 
 In addition, a red signal alerting a driver should have gone off, forcing the driver to apply the brakes. 
 
 Preliminary information indicates some of the cars on that eastbound train were undergoing maintenance in the rail yard, sources said. How the trains managed to leave the yard and travel past the Forest Park terminal and down the tracks to the next stop at Harlem remained unknown. 
 
 The conductor of the westbound train saw the approaching train and did what he could to alert passengers to take over or brace themselves for impact. 
 
 That conductor walked away from the accident, but did have some facial injuries. 
 
 Service was suspended between Forest Park and Austin Avenue, along the border of Chicago and Oak Park. Service was eventually resumed to Forest Park, but trains were not stopping at Harlem. 
 
 Images from Chopper 2 HD showed people being taken to ambulances on stretchers. 
 
 The CTA was providing shuttle buses to transfer affected Blue Line riders to the Green Line. ||||| Questions loom following Blue Line crash, including who started the runaway train, and why didn't a system set up for such an occurrence automatically stop it? Phil Rogers reports in this NBC 5 Investigates segment. (Published Monday, Sept. 30, 2013) 
 
 More than 30 people were injured Monday morning after two trains running on the Chicago Transit Authority’s Blue Line tracks collided, CTA officials confirmed. 
 
 The accident happened just before 8 a.m. at Harlem Avenue and Interstate 290 in suburban Forest Park. A westbound train that stopped at the Harlem station was struck by an out-of-service train heading toward the Loop, officials said. 
 
 CTA officials said 33 people were transported to nine area hospitals. Forest Park Mayor Anthony Calderone told reporters most of the transported riders complained of neck or back pain. 
 
 Police initially treated the area as a crime scene because the out-of-service train may have been stolen, sources said, but the CTA disputed the train was taken without authorization. The National Transportation Safety Board has since taken over the investigation. 
 
 CTA on Collision: 'More Questions Than Answers' 
 
 Chicago Transit Authority spokesman Brian Steele talks to reporters about the train collision on the CTA's Blue Line Tracks. "There are more questions than we have answers at this point," he said. (Published Monday, Sept. 30, 2013) 
 
 "We're exploring everything," an NTSB spokesman said. "We want to establish that the signal system worked, that's the first thing you want to rule out. Then you want to rule out mechanical issues ... then you look at operations." 
 
 Robert Kelly, of Amalgamated Transit Union 308, said it's still unclear what happened and how the train got out of the station. 
 
 "Both the supervisor in the station at Forest Park and the motorman who was sitting in the station said there was nobody on the train as it went through and collided with the other train," Kelly said. 
 
 Rail Union: CTA Collision 'Baffling Everybody' 
 
 Amalgamated Transit Union president Robert Kelly tells reporters no one was on the out-of-service train that collided Monday with another train on the Blue Line tracks. "This is baffling everybody," he said. (Published Monday, Sept. 30, 2013) 
 
 "This is baffling everybody," he said. 
 
 CTA spokesman Brian Steele said there are more questions than answers as staff reviews surveillance video and talks to employees. 
 
 "We don't know what the circumstances are that led to this train to begin moving on the path that it did," Steele said. "It shouldn't have done so and the question of why is what we're looking into." 
 
 10 Dramatic Train Crash Photos 
 
 Blue Line service between Forest Park and Austin was suspended after the incident, and shuttle buses were in place. 
 
 NBC 5 Investigates has learned that the train began its journey at the CTA's Forest Park yard, where it had been parked and awaiting service since Sept. 23. 
 
 By the time it traveled the short distance to the Forest Park station on Monday morning, eyewitnesses said they saw nobody in the motorman's cab. 
 
 RAW: 2 CTA Trains Collide on Blue Line 
 
 Two CTA trains collided just after 8 a.m. Monday on the Blue Line tracks. (Published Monday, Sept. 30, 2013) 
 
 It's believed to have continued on, unmanned for about half of a mile to the spot where it collided with the other train car. 
 
 "That train never should have made it to the Forest Park station. It should have been tripped in the yard," Kelly said. 
 
 Someone had to start the train, and even if they bailed out, it had to travel up an incline and pass through three different fail safe systems designed to stop it. The last fail safe is located in the cab itself, designed to alert a motorman of impending danger ahead. 
 
 Forest Park Mayor On CTA Train Collision 
 
 Forest Park Mayor Anthony Calderone talks to reporters about a train collision on the CTA Blue Line. He said 48 people were taken to about 10 area hospitals. (Published Monday, Sept. 30, 2013) 
 
 "It's a red indication in the cab, when you are approaching something, another train or object, a broken rail, that goes off," Kelly said. "The motorman has to go brake within seconds. If they don't go to brake, the automatic train control will cut them off, and the train is supposed to come to a stop." 
 
 All El trains work from a common key, and sources tell NBC 5 Investigates that there are a lot of train keys out there unaccounted for. 
 
 It could explain how the train was started, but not how it was able to travel across so many safeguards designed to stop it without someone aboard. 
 
 Sources Say Train May Have Been Stolen 
 
 A CTA Source tells Phil Rogers that authorities are working under a theory that the train was hijacked. (Published Monday, Sept. 30, 2013) 
 
 It's also unclear why no one in the CTA command center saw the disaster coming. 
 
 "We have people working in these yars all over the system, and if we have trains that can start moving on their own, our people are in danger out there," Kelly said. 
 
 Witnesses said at least one person was taken away on a stretcher, but the CTA tweeted the injuries were "minor." 
 
 Loyola University Medical Center confirmed they received four patients from the collision but said their injuries were "not serious." 
 
 "I went forward and caught the rail," one passenger said. "I jammed my hip, my feet and my leg." 
 
 Westlake Hospital in Melrose Park said they were treating two patients in good condition and West Suburban Medical Center in Oak Park reported they received one patient in good condition. 
 
 Martinez Butler, a locomotive engineer for another train company, was standing at the corner when the trains collided. 
 
 "There was a train that was stopped at the station. Another train came through and looked like it blew the signal, because I heard beeping," she said. "I'm a locomotive engineer. I know the systems, I know the sounds. When you hear those beepings it's warning you that there is an obstruction in front of you and you need to stop." 
 
 More from NBC Chicago:
– An out-of-service Chicago "L" train plowed into a parked, outbound one today at a Blue Line stop in Forest Park, sending at least 33 people to nine different area hospitals (the local mayor's office puts that number at 48 people in 10 hospitals). The train was moving the wrong way along the track, the Chicago Tribune reports. No passengers were aboard the moving train at the time, and police are investigating the possibility that it may have been stolen, according to CBS 2. None of the injuries is considered serious. One locomotive engineer who saw the collision at the Harlem stop described it to NBC 5 this way: "There was a train that was stopped at the station. Another train came through and looked like it blew the signal, because I heard beeping. I know the systems, I know the sounds. When you hear those beepings it's warning you that there is an obstruction in front of you and you need to stop."