In the last few weeks I've gotten a few emails from folks who have been on an Orange Line train that suddenly became a Brown Line train during rush hour, and vice-versa. The common question being, what's up with that?
The good news is, you are not hallucinating. Here's what the CTA has to say about it:
The capacity at the Midway terminal, which serves the Orange Line, is larger than that of the Kimball terminal, which serves the Brown Line. Under the current schedule, Orange Line rush hour summer service doesn't require as many eight-car trains as the Brown Line. As a result since the schedule went into effect on Aug. 3, one Orange Line train is used on the Brown Line during the morning and evening rush. When it completes its run on the Brown Line it returns to Midway as an Orange Line train.
Operators are supposed to announce the train is operating on the Brown Line when it is between Kimball and the Loop.