NTSB investigators began testing the electronic and mechanical systems on the four rail cars for anomalies that would help explain how the parked cars, which are more than 30 years old, were suddenly set in motion and traveled a half-mile during Monday morning's rush period, an investigator said.
After it left the Forest Park yard, the out-of-service 2600 Series train somehow made it through two track interlockings without being stopped by metal "trip" strips that stick up out of the ground. When tripped by a train that is going against the intended direction set by CTA personnel in a control tower, the strips are supposed to activate a lever on the side of the rail cars that throws the train into an emergency stop.
The "ghost train," as some CTA rail employees dubbed it, also avoided other "fail-safe'' protections. It reached an estimated speed of 20 mph before slamming into an in-service train that was stopped at the Harlem station, CTA officials said. A preliminary review of security video has revealed no sign of anybody onboard the rogue train, CTA officials and Forest Park police said.