Many changes occurred in the ﬁrst half of the 20th century, including the introduction of the one-man streetcars in 1921 and, on April 17, 1920, the debut of the ﬁrst gasoline motor bus on W. Mitchell Street. Trackless trolleys (rubber-Dred electric buses) were substituted for streetcars beginning in 1936 when the North Avenue line was converted to trackless trolley operation. But it wasn’t until 1949 that the last two-man streetcar was retired. Finally, in 1950 the ﬁrst diesel buses were put in to operation.
In December 1952, the complete separation of the transit operation from the electric utility was accomplished when it was sold to a private company, Milwaukee & Suburban Transport Corporation. Under the new ownership, the conversion of the streetcar lines to bus lines was rapidly completed. On March 2, 1958, the last streetcar crossed the Wells Street viaduct and on June 20, 1965, the company converted the two remaining trackless trolley routes to diesel bus routes.
In March 1964, shortly after completion of the ﬁrst freeway link to the suburbs, a new rapid transit bus service called the Freeway Flyer was instituted. The Freeway Flyer proved to be an instant success running between Mayfair Shopping Center in Wauwatosa and Downtown Milwaukee. The Freeway Flyer proved it could attract automobile drivers back to buses. Its popularity grew and today there are numerous Freeway Flyer routes in operation.