The National Transportation Safety Board has officially taken over the investigation.
The NTSB is in Chicago despite the fact there were no fatalities or serious injuries in the accident. But NTSB officials are saying they're not on the scene simply because of worries about systemic problems with the CTA.
A re-enactment was performed on Thursday as to the movement of the train prior to and up to the derailment. The re-enactment signal data was collected to be compared with data at the time of the derailment.
"We're still evaluating it. We're trying to figure out, the way he was operating the train, what would require him to communicate control," said Tim DePaepe of the National Transportation Safety Board.
Investigators are trying to determine what could have prompted the train's 31-year veteran driver William Jones to drive through a red light and move his train beyond a safety switch, which tripped as it was designed to do according to the re-enactment.
After the derailment, the two lead cars of a four-car train perched on a rail more than 20 feet above the ground jumped the tracks near 59th and Prairie, injuring more than a dozen people and causing dozens more evacuations.
Jones, who is not working anymore and whose salary has been suspended, has been tested for drugs and alcohol.
While some passengers say after what happened they don't feel comfortable taking the el, many Green Line El riders found a somewhat normal morning rush hour despite Wednesday's derailment.
"Unfortunately, things happen, you know, but everybody was ok, so that was great," said Laura Davis, Green Line commuter.
Shuttle buses remained at the ready Thursday on the Cottage Grove branch of the Green Line as authorities continued to investigate exactly what went wrong Wednesday afternoon
Thursday morning, trains were back up and running to and from 63rd and Ashland as transit officials blamed operator error for the accident. A CTA spokesperson says the train operator made two key errors, first by failing to heed a red stop signal. Although that tripped an automatic shutdown of the train, they say the operator's second mistake was moving the train across a track switch, causing the derailment.
The incident has some commuters questioning the safety of the city's public rails.
"I got no other way to get around so I got to take the bus," said Lisa Catchings, CTA rider.
The union representing the operator says they are waiting for the full reports of the investigation, but those other operators who know this particular operator say that he is a conscientious individual who has had some 31 years on the job. Other operators who asked not to be identified have said that they are questioning that area of the junction, saying that they have had problems there before. They also are questioning whether that red signal light was working.