Legally, the CTA is not supposed to be controlled by the mayor’s office. It is an independent (in theory) government agency created by the State of Illinois, and is tasked with transportation in Cook County beyond just the city of Chicago. Up until a few years ago, there were a couple of suburb-only bus routes, and if you consider that Howard Station is really on the border, you can add several other bus routes and two rail lines (not counting the rush hour Purple Express) that operate largely suburb-only.