The 20th century transformed public transportation through technological advancement and changing urban needs. Motorized buses gradually replaced streetcars in many cities, offering greater route flexibility without fixed rail infrastructure. Major metropolitan areas invested in comprehensive subway and metro systems, with Tokyo, New York, Moscow, and London developing some of the world's most extensive networks. The post-WWII era initially saw public transit decline as automobile ownership surged, but the energy crises of the 1970s renewed interest in efficient mass transit. High-speed rail emerged as a transformative technology, beginning with Japan's Shinkansen in 1964 and later expanding throughout Europe and Asia, offering competitive alternatives to short-haul flights. The 21st century has brought renewed focus on sustainability and efficiency, with innovations like bus rapid transit systems, self-driving vehicles, and Mobility-as-a-Service platforms integrating various transportation modes through digital applications. Many cities are now investing in light rail systems, electric bus fleets, and bicycle-sharing programs to create multi-modal networks that reduce congestion and emissions. The future points toward increasingly connected and autonomous systems, with experimental technologies like vacuum tube transport (Hyperloop) and aerial mobility solutions promising to redefine the boundaries of public transportation in coming decades. Shutdown123