I came across this map from the Detroit Transit History website and immediately thought of The Detroit Bus Company.

Organized back in 1919 by Herbert Y. McMullen (an automobile accessory and supply distributor), the Detroit Motorbus Company would become the first permanently successful transit bus company to provide motor coach service within the city of Detroit.  To help gain the support of the public as to the type of service it would be providing, the company began operating a sample prototype double-decker bus on demonstrator trips to hotels, banks and department stores within the central business district, and along Woodward Avenue.

It is hard to imagine a time when buses did not traverse the city of Detroit, but largely up until 1924 public transportation was all street railways. The Department of Street Railways (DSR) began its first bus lines in 1925. By 1930, the Detroit Motorbus Company (DMB) was running 395 buses within the city and the suburbs. In 1931, the city began negotiations with DMB to takeover its operations as a way to eliminate competition. By 1932 many of the DMB lines had been taken over by the city and many of the DMB’s suburban lines still exist as SMART bus lines today.