It's always difficult to be forced to place blame in a situation like this, but as of the reports currently trickling in at the time of this writing, it appears that even the union for train conductor's are willing to admit that the conductor was not operating at his fullest capacity at the time of the derailment.
I think it was more likely to be the train conductor's fault than a faulty train, because it is pretty hard to explain how a train ended up going all the way up an escalator at the speed it was traveling. The train would have had to have been traveling well above the speed limit at a station in order for that to have happened. It was likely the operator's fault.
I think that it was her fault especially if they have came to terms that she dozed off. If there was a faulty issue she would not have known because she was dozed off at the time. In this incident I think that the conductor has some fault in this.
I have my doubts the Chicago derailment was due to the conductor, it was more than likely caused by a faulty train. Employees are more than likely interested in keeping their decently paid jobs rather than throwing their career down the train. The train system in Chicago is old and so are the trains.