The Chicago area was no exception to this trend. Although the Chicago Transit Authority (CTA) has existed since 1947 as a public agency providing rapid transit and bus service within the city of Chicago, the CTA was originally intended to be self supporting. Private railroads continued to provide commuter rail service in the area, while private bus companies operated in the suburbs.
On March 19, 1974, voters in the 6 county Chicago metropolitan area approved the creation of the Regional Transportation Authority (RTA), to subsidize and coordinate public transportation within the entire metropolitan area. Originally, the RTA entered "purchase of service agreements" with the various private transportation operators. RTA would set schedules and fares and other policies, while contracting with and subsidizing the private companies which would actually operate the services.
In 1984, the RTA was reorganized, and became primarily an oversight agency over 3 separate operating agencies, each with their own boards. The CTA continued to exist for the city of Chicago, while two new agencies were formed. Metra would be the agency responsible for the commuter railroads, while Pace would be responsible for the suburban buses. Metra and Pace eventually assumed direct operation of most of the commuter railroads and private bus companies.
Link to official RTA Web Site.