Leading up to the consolidation of the 'L' companies into the CRT was decades of the Chicago Elevated Railways Collateral Trust (CER), an entity directly attributed to utilities magnate Samuel Insull.

The CER laid the groundwork for the companies to become one, including financial agreements and simplification that allowed for free transfers between the various lines at the places where they shared facilities, such as at Loop elevated stations.

[2] These predecessors include: The CRT network was entirely at or above grade level until the 1943 opening of the State Street subway, now part of CTA's Red Line.

Following World War II and the continuing financial malaise of the privately owned bus, streetcar and elevated/subway operators, both the city government of Chicago and the Illinois legislature favored consolidating the three separate systems into a single, public-owned authority.

The assets and operations of the CRT were assumed by the newly established Chicago Transit Authority on October 1, 1947.