CHICAGO — Thursday’s CTA derailment is not the first time trains on that section of the Green Line have had problems.
Everything from human error to track conditions and switching problems can cause a train to leave the tracks.
Despite several incidents in the last decade, the CTA insists the Green Line isn't more accident prone than any other line on the system.
There have been at least four train derailments on the Green Line in the last 11 years. None resulted in death and no train cars actually fell from the elevated line.
The most recent was August 2015. The third car car of a four car train went off the tracks near 61st Street, about a dozen blocks from Thursday’s derailment.
Like Thursday’s incident, the most precarious point came when firefighters had to use ladders to get nearly 80 passengers down.
Experts said the most frequent cause of a derailment is a switching problem, where tracks meet.
An errant switch can send the front of a train in one direction and the rear in another.
Back in May of 2008, was the most serious Green Line incident in which several cars left the tracks in different directions.
The CTA blamed the train operator for ignoring a signal to stop.
Passengers said they feared for their lives
A CTA spokesperson issued a statement to WGN Investigates and said: "The Green Line carries hundreds of trains each week, tens of thousands each year, and has not had any more derailments than any other line. Like all CTA rail lines, the Green Line is safe. There is no known link between any of the incidents mentioned besides the train line and there has been no reason to question the safety of the line."
The National Transportation Safety Board is generally not called in to investigate derailments like the ones that have hit the Green Line. Instead, they count on the CTA to handle the probe and make appropriate safety changes.