Replacement Eastern span replacement of the San Francisco–Oakland Bay Bridge

artist s rendering of basic viaduct-style span, known skyway design (1997)

engineering , economic analysis in 1996 suggested replacement bridge cost few hundred million dollars more retrofit of existing eastern span, have far longer expected useful life (perhaps 75 100 years rather 30), , require far less maintenance. rather retrofit existing bridge, caltrans (california department of transportation) decided replace entire eastern span. design proposed elevated viaduct consisting of reinforced concrete columns , precast concrete segment spans seen in illustration @ right. design criterion new bridge should survive 8.5 magnitude earthquake on of several faults in region (particularly nearby san andreas , hayward faults). aesthetics of proposal not received either public or politicians, being characterized freeway on stilts .

original , final eastern span signature bridge proposal



artistic rendition of accepted design seen treasure island after removal of original span (ca. 2018)

after this, design contest held signature span (a span distinctive , dramatic appearance, unique site) engineering , design advisory panel (edap) of metropolitan transportation commission (mtc). number of innovative proposals examined until 4 proposals submitted members of edap selected semi-finalists, , winner selected group. posed serious conflict of interest, members of edap selecting bridge design reviewed proposals own firms , rejected proposals did not have representative on edap. design chosen more expensive alternatives, because primary structure cannot self-supporting until structurally complete. requires building of 2 bridges, first falsework support final span, removed upon completion of final span. has been criticized both less structurally robust design , less predictable construction costs other modern spans.

alignment

in 1997, there political bickering on whether bridge should built north or south of existing bridge, mayors brown (san francisco s willie brown , oakland s jerry brown) on opposite sides of issue. yerba buena island within city limits of san francisco , proposed (and current) northern alignment cast shadow on prime development sites on island s eastern shore. u.s. navy (at time controlling authority of island) involved @ behest of san francisco in restricting caltrans soil engineer s access proposed site. may have caused two-year delay , many hundred millions of dollars in additional costs.

various options determined worthy of consideration , examined jointly state , federal authorities, input united states coast guard.

grade alternatives included:

extending sea level approach grade westward, steep approach span.
using relatively constant grade, including on portion of span.
using relatively constant grade near span, span level.

the last alternative chosen because considered have superior visual effect , improved driving experience. grade of new approach channel span less of previous structure , less ship clearance provided under span owing depth of deck box structures.

alignment alternatives in 1998

alignment alternatives included (see image @ right details):

s4: southern alignment, curved, shorter route northern alternatives.
n2: two-bend northern alignment close existing bridge.
n6: single bend alignment, main span tending northward curve eastern approach viaducts, being parallel existing double-deck truss causeway approach.

the last alternative selected, presents superior view of san francisco west compared others views obscured yerba buena island. more northerly track encounter more difficult geotechnical circumstances.