CHICAGO (AP) - Nearly a week after an unoccupied Chicago Transit Authority train rumbled down a track for nearly a mile and struck another train head-on, investigators were still trying to determine Friday how and when the unoccupied train was powered up.
In a report, the National Transportation Safety Board also said Friday the train was able to make its way through five stop mechanisms because a "master lever on the operator console had been left in a setting that allowed the train car brakes to recover and reset." That allowed the train to start rolling over and over again until it crashed into another train.
A few dozen people were taken to area hospitals and were treated for minor injuries.
The three-page NTSB report does not include any conclusions about how the train was powered. But CTA spokesman Brian Steele said Friday there was "no indication at this point that there is any type of sabotage or vandalism involved in this incident."
Steele said there were no broken windows or anything else that might suggest someone broke into the train and there were no reports of any suspicious activity in the rail yard before the train started moving Monday morning.
The report makes a number of "urgent safety recommendations." But Steele said the CTA had already taken those steps earlier in the week. He also said the CTA ordered that battery cables in out-of-service trains be disconnected "to prevent them from being powered up." Steele said the CTA is taking steps to make sure that one car cannot power up another when they are coupled, as can happen now.
The train was in a service yard awaiting repairs when it left the parked area, went past a turnaround and through another station before the accident at the station in Forest Park, about 10 miles west of Chicago.
Video footage shows that no one was driving the four-car train.
The Blue Line connects Chicago's near-western suburbs with the city's downtown and O'Hare International Airport.
The investigation into what caused the crash is continuing.