The CTA's efforts at spin-control with this are quite comical. CTA is trying to downplay the seriousness of the issue saying it wasn't a detailment, just a "split-switch issue" which IMHO can be far more serious.
Media reports are unclear but from the video and description, it appears the lead truck of a SB train went the wrong way on a crossover with the rear truck and the rest of the train going the way the switch was set. And while technically all wheels were on "A" rail, they all weren't on the correct rail. With the car split between two tracks, the car was completely outside the "clearance envelope". In a tunnel or at an overpass, the car could have found itself wrapped around a support column. So yes, far more serious than a simple derailment where the wheels stay next to the rail.
And then to make it worse, from <http://www.chicagotribune.com/news/loca ... 5146.story
>, "The operator immediately recognized the problem and stopped the train, [CTA spokeswoman Tammy] Chase said. The operator then walked to the last car of the train and tried to back up the train to get the front car off track No. 3 and off the crossover switch and back onto track No. 2, Chase said." What? The operator just tried to back up???!!! The front truck that picked the switch just ran through the other end of the crossover and the operator somehow thought just back up and all would be right? From the video (this was a SB train but the video starts with the train north of the crossover), it appears it was backed all the way to the other side of the crossover. At this point, coming back through the run-through switch, they're probably very lucky not to have really derailed. Snagging on third rail in the crossover was also a possibility.
It's not clear if the operator did this on his/her own or with permission but it still strikes me as very, very stupid.