The Chicago Central Area Transit Plan, generally referred to as the Chicago Central Area Transit Project (CCATP) in the 1970s, was an extensive study of the rapid transit system in downtown Chicago; the study had begun in 1965. Volume 2 included detailed preliminary plans, architectural, and engineering drawings, which were to be the basis for construction contracts for the proposed loop and distributor subway systems. Volume 3 detailed supplemental data gathered during the study phases.