Some of the Bay Area Rapid Transit system's current coverage area was once served by an electrified streetcar and suburban train system called the Key System. This early 20th-century system once had regular transbay traffic across the lower deck of the Bay Bridge, but the system was dismantled in the 1950s, with its last transbay crossing in 1958, and was superseded by highway travel. A 1950s study of traffic problems in the Bay Area concluded the most cost-effective solution for the Bay Area's traffic woes would be to form a transit district charged with the construction and operation of a new, high-speed rapid transit system linking the cities and suburbs. Marvin E. Lewis, a San Francisco trial attorney and member of the city's board of supervisors spearheaded a grassroots movement to advance the idea of an alternative bay crossing and the possibility of regional transit network.