By the 1980s, three rapidly growing areas in California - Silicon Valley, the Tri-Valley, and the middle part of the Central Valley - were poorly connected by public transit, even as Interstate 580 and Interstate 680 became more congested.
The three areas had connections to San Francisco and Oakland via Caltrain and the Amtrak San Joaquin (and later BART and Capitol Corridor trains), but commuting from the Central Valley and Tri-Valley to Silicon Valley required using a car or limited bus service. In 1989, the San Joaquin Council of Governments, Stockton Chamber of Commerce, and the Building Industry Association of the Delta started work on a 20-year transportation plan for their section of the Central Valley. In November 1990, San Joaquin County voters passed Measure K, a half-cent sales tax to fund a variety of transportation improvements.
The highest-priority project was the establishment of passenger rail service to San Jose.