Greyhound Lines, the predominant intercity carrier in the United States, surpassed the passenger volume of all Class I (large) railroads in 1935. Due to anti-competition regulations enacted by the Interstate Commerce Commission, Greyhound was effectively granted a monopoly on many of its routes, particularly in the lower-demand Midwest.
At the same time many transit systems were in financial disarray, the Civil Rights Movement was reaching its peak. In 1955, Rosa Parks refused to relinquish her seat on a National City Lines bus in Montgomery, Alabama to a white customer. Her actions sparked protests nationwide and an outright boycott of the local private bus company for a year, until a Supreme Court decision ruled that race-based segregation on buses was unconstitutional. Transportation segregation shifted from being seat-based to mode-based; instead of sitting next to black residents, white residents fled Montgomery, Alabama and other American cities for the suburbs, where few black residents resided.
In part due to the affordability and attractiveness of new suburban developments in The '50s, as well as the passage by Dwight D. Eisenhower of the National System of Interstate and Defense Highways, local transit ridership plunged dramatically. Compounded by regulations that imposed comparatively high tax rates on privately-operated electric traction railways and declining ridership, many lines were converted to bus operations throughout the 1950s and 1960s. At first, and to a large extent still today, these operated on the same streets open to drivers of private cars meaning the bus could and did get stuck in traffic, removing a key advantage of mass transit for passengers already aboard and adding to wait times for those the bus hasn't yet reached.
