page_title: Southern Crossing (California)
section_title: Fourth proposal (1953–58): Potrero Point to Bay Farm Island
hierarchical_section_title: Southern Crossing (California) / History / Fourth proposal (1953–58): Potrero Point to Bay Farm Island
caption_attribution_description: English: Southern Crossing, Bay Tube section
context_page_description: The Southern Crossing is a proposed highway structure that would span San Francisco Bay in California, somewhere south of the San Francisco–Oakland Bay Bridge and north of the San Mateo–Hayward Bridge. Several proposals have been made since 1947, varying in design and specific location, but none of them have ever been implemented because of cost, environmental and other concerns.
context_section_description: In 1953, the legislature passed a bill to build the Southern Crossing with the alignment spanning from San Francisco near Third and Army Streets (Potrero Point )to near Bay Farm Island  in Alameda. The western approaches would include connections to the Bayshore Freeway at 26th Street; the Southern Crossing would also connect with a proposed future freeway at Army Street and an extended Embarcadero Freeway. At the eastern end, the southern crossing would connect to the Alameda County road along the bayfront near its intersection with Kilkenny Road. The Southern Crossing alignment specified by the legislature had not been previously studied in the 1941 and 1947 reports.
  After the Southern Crossing Bill was passed, at a public hearing held on August 17, 1953, the Navy announced plans to extend its seadrome runways south from NAS Alameda, which would interfere with the planned direct alignment of the Southern Crossing, and the Department of the Army subsequently denied the Southern Crossing application on November 3, 1953. A revised alignment was designed to route around the restricted area, and the Army granted a construction permit on April 8, 1954, contingent on the construction to start within five years and complete within ten.
  In the 1954 Progress Report, the approved design for the Southern Crossing was largely a low-level causeway not to exceed 40 feet (12 m) in height to avoid seadrome interference, although the eastern approach would provide a vertical clearance of 15 feet (4.6 m) to allow the passage of crash boats from NAS Alameda. A tube section would be built across the navigation channel to allow the passage of ships deeper into the Bay. Traffic would be carried in six lanes, divided into two three-lane causeways and three two-lane tubes, and grades would be limited to 3​¹⁄₂%. The total planned length of the 1954 Southern Crossing was 40,730 feet (12,410 m).
  According to the 1955 Progress Report, the preliminary plans had been completed and updated cost estimates were available. In March 1956, the 1955 Supplement report was issued covering the legislative amendments made that month changing the San Francisco approaches to the Southern Crossing.
  The Southern Crossing design was updated again in October 1956; the 1956 Progress Report detailed further changes to the San Francisco and Bay Farm Island approaches mandated by legislative action. By 1956, the Southern Crossing was ready to post requests for bidding; because there was "considerable opposition to raising tolls on the Bay Bridge" from their current US$0.25 (equivalent to $2.35 in 2019), the cost of the Southern Crossing meant the project would have to be built in stages. The overall length of the Southern Crossing was reduced slightly to 39,910 feet (12,160 m) with the revised approaches, but retained the same basic structure: two three-lane roadways carried on mole and viaducts, with a three-tube (each with two unidirectional lanes) section crossing the navigation channel. In San Francisco, the northern approach would connect with the Embarcadero Freeway; the southern approach would connect with the Southern Freeway, and the direct connection with the Bayshore Freeway was dropped. Both approaches would be double-decked, with three unidirectional lanes per deck. On Bay Farm Island, the Southern Crossing would split into two separate approaches at the Bay Farm Island Bridge; the two would then would connect with the Eastshore Freeway and the Posey and Webster Street tubes. In addition, the 1956 Progress Report considered the effect of the Southern Crossing on traffic over the San Mateo–Hayward Bridge (acquired by the State of California in September 1951) as well as the planned Transbay Tube.
  To explore the financial feasibility further, DPW commissioned a study from Smith Barney & Co., which concluded "the Complete Southern Crossing is not feasible as presently authorized at a basic toll rate of 25 cents for both the Bay Bridge and the Southern Crossing"; the California Toll Bridge Authority then directed Bay Toll Crossings to develop a Minimum Southern
caption: Typical Bay Tube section (1956)
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