(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. A westbound train that stopped at the Harlem station was struck by an out-of-service train heading toward the Loop, officials said. At least 33 people were hurt when the trains collided in west suburban Forest park, according to the CTA. 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. 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. 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. Investigators will determine whether the fail-safe trip mechanisms failed and if the switches were properly aligned, CTA spokesman Brian Steele said. 10 Dramatic Train Crash Photos 
 
 Blue Line service between Forest Park and Austin was suspended after the incident, and shuttle buses were in place. 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.  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. (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. 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. 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. The cab signal gives the operator about 2 seconds to reduce speed before it automatically applies the brakes. 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. 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. "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." “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. 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?'" 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.
– 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."