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.
History
Origins The idea for the Southern Crossing dates back to the 1940s when several additional bridges across San Francisco Bay were studied. After the Bay Bridge crossing opened in 1936, connecting Rincon Hill in San Francisco with the Key Mole in Oakland via two high-level bridges and a tunnel through Yerba Buena Island, vehicle traffic exceeded estimates almost immediately; by 1945, even with gasoline rationing, traffic was 191% of the estimates made during planning, and would reach an average of 69,000 vehicles per day by 1946. A second crossing was deemed necessary and studies were initiated to determine the best location and configuration.
First proposal (1941): Hunters Point to Bay Farm Island A study completed on November 18, 1941 conducted by a joint Army-Navy Board concluded that a high-level bridge between Hunters Point and Bay Farm Island was feasible at an estimated cost of $53.2M. The high-level bridge was preferred to a low-level lift bridge. The western terminus would have been on the south side of the existing Hunters Point Naval Shipyard and the eastern terminus would be on the southwest shore of Bay Farm Island. However, no immediate need was identified for a new bridge, and the project was shelved.
Second proposals (1947): Parallel Bridge and Southern Crossing Southern Crossing: Potrero Point to Alameda
On January 25, 1947, another joint Army-Navy Board published a study which concluded that a combination of causeway and tube from San Francisco (near Army Street/Potrero Point ) to Alameda was preferred. From Alameda, the route would run north through the Posey Street tube to a point in Oakland near the present-day western terminus of Interstate 980. This was essentially the same as alternative no. 12 from the contemporaneous California Department of Public Works (DPW) study. Both routes recommended by the two 1947 studies were endorsed by Charles H. Purcell, the director of the California DPW on November 10, 1947; however, because of limited budget, the more expensive Southern Crossing option would be built after the Parallel Bridge.
During the development of the Joint Army-Navy Board study, a public meeting was held on August 13, 1946, where ten alternative alignments for a second crossing were suggested. One group, based in San Francisco, advocated for a low-level causeway allowing the extension of the transcontinental rail line from Oakland; another group, based in the East Bay, proposed a high-level span for automobiles only. The California state government, represented by engineer F. W. Panhorst, agreed with the East Bay group and further advocated that to provide the maximum reduction in traffic on the Bay Bridge, the western terminus should be on Telegraph Hill or Rincon Hill . The August 1946 meeting was also notable for the first public presentation of the Reber Plan, which called for an immense dike between San Francisco and Oakland wide, reclaiming of land from San Francisco Bay and eliminating the need for another bridge. The 1947 Joint Army-Navy Board considered 29 different alignments before concluding the causeway-tube was the preferred option.
Parallel Bridge The first of the California state government studies was published a week later, on January 31, 1947, which concluded that another trans-Bay crossing was feasible and recommended that it be located close to the existing Bay Bridge. This alignment was later named the Parallel Bridge.
The main reason to duplicate the existing route was to provide immediate relief to Bay Bridge traffic; the crossing further south from Potrero Point to Alameda was estimated to divert only 20% of existing traffic, and the southernmost proposal studied, from Hunters Point to Bay Farm Island , was estimated to divert only 5% of existing traffic. The alternative western terminus at Telegraph Hill was rejected on the basis of existing traffic patterns and freeway connections, and the alternative eastern terminus on the S.P. or Oakland Mole was rejected not only because it would require a long high-level span to avoid interference with the existing shipping channel, but also that such a span would also interfere with flight operations at Naval Air Station Alameda.
The 1947 study also determined the feasibility of extending existing railroad termini for the Western Pacific Railroad, Atchison, Topeka, and Santa Fe, and Southern Pacific from Oakland to San Francisco; of the three, SP already had the option of using the Dumbarton Cut-off, and WP and AT&SF used buses (for passengers) or ferries (for freight); both a high-level bridge and a tunnel were ruled out as the required grades for the high-level bridge could not be achieved without excessively long approaches, and the tunnel would require conversion to electric locomotives. However, a low-level bridge accommodating rail traffic was considered for the southernmost Hunters Point to Bay Farm Island crossing as alternative no. 11.
Alternative no. 5 would have used parallel tubes on a continuous radius curve of , providing the shortest overall distance at . Each concrete tube would be in outer diameter, and would be built on land in segments, which would each be floated into position then sunk in place. Ventilation would be provided through the roadway space, connected to ventilation structures at the two termini. A similar underwater route, with termini at the Market Street subway (slightly north of Rincon Hill) and the S.P. Mole was eventually built as the Transbay Tube for BART in the 1960s.
Alternative no. 7 included what would have been the longest suspension bridge in the world for the western portion, slightly longer than the Golden Gate Bridge at long overall, composed of a main span flanked by two side spans. Of all the alternative options studied in 1947, no. 7 had the shortest distance to span on the western portion.
Four true southern crossings were studied in 1947 (alternatives no. 10, 10A, 11, and 12). 10 and 10A differed in the configuration of the lower deck; 10 called for two truck lanes and two railroad tracks, while 10A omitted the tracks entirely. Both 10/10A and 12 included the cost of an additional tube to augment the existing Posey tube from Alameda to Oakland, which was eventually constructed as the Webster Street tube in 1963. Alternative no. 11 devoted the lower deck entirely to four railroad tracks, as the anticipated vehicular traffic was low. It included a long vertical lift span. Alternative no. 12 would use four tunnels on the western half, each containing two lanes of traffic, approximately long overall to provide a wide navigation channel; the eastern portion of the crossing would be at the water's level, consisting of a trestle long and a mole long.
+ Proposed second trans-Bay crossing study alternatives (1947) No. Western terminus via Eastern terminus Structure Cost West East 2 Telegraph Hill Yerba Buena Island Key Mole Four-span suspension bridge Truss/cantilever bridge $103M 3 S.P. Mole $102M 4 Key Mole $105.4M 5 Rincon Hill — S.P. Mole Two or more tubes $167M 6 Telegraph Hill Yerba Buena Island S.P. Mole Four-span suspension bridge Truss/cantilever bridge $101M 7 Key Mole Three or four-span suspension bridge $134M 8 Rincon Hill Key Mole Twin of existing Bay Bridge, to the north $84M 9 S.P. Mole Twin of existing western span Truss/cantilever bridge $103M 10 Potrero Pt — Alameda Truss/cantilever bridge $108M 10A $83M 11 Candlestick Pt Bay Farm Island Steel with lift across channel $130M 12 Potrero Pt Alameda Mole, viaduct, and tube $137M
The California Department of Public Works created the San Francisco Bay Toll Crossings Division in December 1947 to study the Parallel Bridge and Southern Crossing proposals in further detail. In 1948, the Toll Crossings Division reiterated that a southern crossing was "entirely feasible" but recommended the expansion of the existing Bay Bridge with the Parallel Bridge alignment instead, which could be completed in 1954 at an estimated cost of . Preliminary plans for both the Parallel Bridge and Southern Crossing were prepared in 1948, which were reviewed by a board of consulting engineers in 1949.
Because both bridges could not be financed simultaneously, the California Toll Bridge Authority resolved to complete the plans for the Parallel Bridge on March 23, 1949. Local and state leaders failed to align their support on a single proposal. In May 1949, San Francisco mayor Elmer Robinson testified before the California State Assembly in support of the Southern Crossing. Director Purcell went before Congress in July 1949 to request permission to expand the right-of-way on Yerba Buena Island to allow construction of the Parallel Bridge. Work on both the Southern Crossing and Parallel Bridge projects was halted on June 30, 1950, after disputes about the priority, alignment, and purpose of a second bridge could not be reconciled. An attempt to revive a second trans-Bay crossing failed to pass the California State Legislature during the 1951 session.
Third proposal (1949, 1989, 1999): Wright/Polivka Butterfly Wing bridge At about the same time, architect Frank Lloyd Wright and engineer Jaroslav Joseph Polivka unveiled the reinforced concrete "Butterfly Wing" bridge in May 1949 before Bay Toll Crossings. The Butterfly Wing bridge was first presented to the public in May 1953 before a sold-out audience at the San Francisco Museum of Art. A long model of the Butterfly Wing bridge was built for the 1953 presentation; it was later displayed locally in shops, malls, and was included in a traveling exhibition before being used as a prop in the 1988 film Die Hard.
Polivka had previously submitted preliminary plans to DPW for a Southern Crossing bridge in February 1947; his initial design featured an immense long concrete arch spanning the navigation channel, which was unprecedented in length, size, and material. Polivka is credited with piquing Wright's interest in bridge design; they began their collaboration later in 1947, resulting in the Butterfly Wing bridge proposal for the Southern Crossing. The Butterfly Wing design was derived from a crossing designed by Wright in 1947 over the Wisconsin River near Spring Green, Wisconsin for the Wisconsin Highway commission.
The final design carries six lanes of traffic over twin long diverging arches providing of vertical clearance above the bay's main ship channel. Another source claims the pair of main arches were long and afforded of vertical clearance. The concrete "tap-root" piers were hollow to add buoyant support to the structure. The original alignment had a western terminus near Third and Army and an eastern terminus on Bay Farm Island . The design included a hanging park and parking in the middle of the arched section, making the Butterfly Bridge a destination in addition to a crossing. Polivka and Wright's design, using reinforced concrete, was designed to be half the cost of a conventional steel bridge, provide lower maintenance costs, and resist earthquake damage. However, such proposals never got beyond the drawing board because of cost concerns.