During the 1930s, 1940s the US had the best public transportation system in the world, but National City Lines, a company with funding from General Motors, Firestone Tire, Standard Oil of California and Phillips Petroleum, bought up hundreds of beloved public urban mass transit systems to privatize them.
The much beloved and energy efficient electric light rail trains occupied tracks which GM felt were blocking the full realization of their vision for the automobile, oil and tire industries. As the saying goes, "What's good for GM is Good for America" so those hundreds of light rail systems were torn up leading to vast increases in the purchasing of automobiles. After all, people had to get to work. Lots of people could not afford cars, however. They rode the new "modern" deisel buses, which unlike the public transit systems were segregated. On December 1, 1955, in Montgomery, Alabama, Parks refused to obey bus driver James F. Blake's order to give up her seat in the colored section to a white passenger, after the white section was filled.
Gradually, ridership fell on the diesel buses and many lines were discontinued due to lack of ridership. The rest is history.