June 11, 1978: The freighter Chavez hits one of the twin steel drawspans over the Duwamish Waterway, leaving the bridge stuck upright for several years.
Aug. 18, 1980: A consortium of four engineering companies issues blueprints for a bridge with a mainspan 590 feet long and 140 feet high.
July 14, 1984: The new six-lane concrete bridge opens.
Aug. 26, 2013: Seattle Department of Transportation (SDOT) structures director John Buswell maps several small cracks in the concrete girders, shortly after they were discovered by a routine inspection.
March 17, 2014: John Clark, a lead designer of the 1984 bridge, issues a brief technical report that lists possible causes of the cracks. He advises the city to seal cracks in epoxy, attach gauges to monitor their width and watch for signs they become “active.” SDOT increases inspections to yearly rather than every two years.
May 28, 2014: SDOT inspectors find that certain exterior cracks, which hadn’t penetrated the girder walls before, “are visible on the inside this year.” Cracks are noted on the south girder and in the side spans.
Jan. 18, 2019: A report by monitoring company BDI documents extensive cracks and proposes more electronic devices to monitor changes.
July 31, 2019: Buswell’s successor, Matt Donahue, asks engineers from the engineering firm WSP whether the bridge should be closed. The engineers conclude it’s safe, but closure could become necessary upon further investigation.
Feb. 21, 2020: As cracks spread, WSP advises the city to reduce the bridge to two lanes each direction and make repairs by the end of 2020.
March 19, 2020: Greg Banks, a WSP project manager, and Donahue discuss the need to close the bridge because accelerating cracks “could lead to collapse.” Some cracks grew two feet in two weeks.
March 23, 2020: Donahue walks through the girders to examine crack spread, then calls a colleague to request an emergency shutdown.
Nov. 19, 2020: Mayor Jenny Durkan announces the city intends to repair the bridge rather than replace the cracked spans.