Gary Railways and Shore Line Motor Coach were subsidiaries of Midland Utilities, a public utility holding company controlled by Samuel Insull. The streetcar system in Hammond and Whiting and East Chicago had meanwhile evolved to Calumet Railways, a separate company. When the Insull companies were dissolved in 1931, Calumet Railways reorganized as Chicago & Calumet District Transit Co., and acquired Shore Line Motor Coach Co., along with Midwest Motor Coach Co., which had also been acquired by Midland Utilities as a subsidiary in 1929. Chicago & Calumet District Transit Co. also acquired Gary Railways, operating it as a separate subsidiary, until selling the company again in 1943.
The last Calumet streetcars were discontinued in 1940. Historical information on the C&CD bus routes has been difficult to obtain, presumably because of a lack of printed timetables or maps. But a special thanks goes to Chicago bus historian Andre Kristopans, for supplying information pertaining to C&CD's bus routes. Kristopans reports that the C&CD local bus route network basically remained unchanged until its demise in 1971. Even though travel patterns had changed. Many routes were designed to serve various steel mills and other area industries, and continued to serve those industries, despite the general industrial decline. The only significant changes to the C&CD route network were the addition of express bus routes to and from downtown Chicago.
During the 1950's and 1960's, the downtown Chicago bus routes used the Greyhound Terminal at Randolph St. and Clark St. By the 1970's, buses instead made downtown stops along Michigan Ave. Some bus routes also served the Greyhound neighborhood station at 6302 S. Stony Island Ave., at the time at the CTA Jackson Park elevated terminal.
After a few years without public transportation in the 1970's, the cities of Hammond and East Chicago were able to invent new bus networks, completely different from the C&CD network.