Streetcar use continued to increase until 1923 when patronage reached 15.7 billion, but it declined in every year after that as automobile use increased amongst the middle and upper classes. By the 1930s, the once-profitable streetcar companies were diversifying by adding motorized buses and trackless trolleys to their fleets. By the 1940s, streetcar ridership had dropped dramatically, and few subdivisions were being built with streetcars or mass transit in general in mind. By the 1950s, nearly all streetcar lines had stopped running, and were instead served by buses.