BART began service in 1972 as one of the first modern rapid transit systems in America. The system was designed to provide a high-speed regional alternative to freeway congestion in the rapidly growing San Francisco Bay Area. BART was groundbreaking in many ways, featuring automated trains, wide-gauge tracks for stability at high speeds, and transbay tube construction. The system has expanded significantly since its initial opening, now serving five counties with over 130 miles of track. Major expansions have included the SFO Airport extension (2003), Oakland Airport Connector (2014), and Silicon Valley extension (2020).