A viaduct timeline

1920s — Debate begins about building a waterfront highway.

1953 — First segment of Alaskan Way Viaduct opens. Battery Street Tunnel and southern extension open six years later.

1989 — An earthquake in the San Francisco Bay Area topples an elevated freeway, killing 42 people. Officials here begin to ponder the aging Seattle viaduct's condition.

2001 — Nisqually earthquake on Feb. 28 prompts a precautionary viaduct closure that gridlocks the city. A few columns begin to sink slightly near state ferry terminal.

January 2007 — Gov. Christine Gregoire's budget earmarks $2.8 billion for viaduct replacement, roughly the cost then of a six-lane elevated highway. Extra money for a tunnel pushed by city officials would have to come from city or regional taxes.

March 2007 — Voters in Seattle reject advisory measures to build an elevated highway or a four-lane tunnel suggested. Gregoire, King County Executive Ron Sims and Seattle Mayor Greg Nickels announce plans to move ahead on parts of the project they agree on: a Sodo interchange, south-end Viaduct rebuild, transit improvements, and safety upgrades to the Battery Street Tunnel.

December 2007 — Gregoire says she's open to surface-transit ideas, after momentum among Seattle leaders shifts in that direction.

April 2008 — Washington state Department of Transportation reinforces four column foundations near the state ferry terminal, which halts the sinking at 5 ½ inches.

June 2008 — State dismisses the idea of retrofitting the existing viaduct, as well as a bridge across Elliott Bay.

November 2008 — State announces new cost estimates ranging from $4.7 billion for a bored tunnel to $2 billion for a surface option. Both figures include $1.2 billion for the Sodo section, transit and Battery Street tunnel. Without much publicity, DOT slims some highway options from six lanes to four, to offset rising materials costs.

Dec. 11 — State narrows the replacement options to two: A "surface and transit" plan and an elevated highway that has two lanes in each direction. A final decision is supposedly due by early 2009.

Sources: Seattletimes.com archives, Historylink.org