It stands for "Chicago transit authority". I don't know about you, but search engines have become useless since last year, I'm talking downright unusable.

https://en.wikipedia.org/wiki/CTA

The Chicago Transit Authority has existed for only about 70 years despite transit in Chicago being around for 125+ years.

Legislation the governor signed last week all but guarantees that it won’t see its hundredth birthday except possibly as a sticker on the side of the busses and trains. Within 5 years the agency will only have the duty to plan routes within the city limits, and maybe do some of the driver hiring.