To preview the traffic mess coming to Seattle in January, it helps to look back to the last traffic closure of the Alaskan Way Viaduct.
For nine days starting on April 29, 2016, state officials closed the aging structure while the machine Bertha drilled a new tunnel for State Route 99 beneath it.
Beginning January 11, 2019, SR99 will close entirely for three weeks as the roadway is realigned from the viaduct to the new tunnel.
The entire impact could stretch for six weeks until all the work is done.
An analysis of the 2016 traffic closure by the Washington State Department of Transportation shows the impacts extended well beyond Seattle.
"The backups begin earlier, they last longer, the travel speeds are lower, it's a pretty big deal," said Bart Treece of WSDOT.
Morning peak travel times between Federal Way and Seattle on I-5 rose from more than 50 minutes to more than 70 minutes.
"Travel times across I-90 doubled, travel times on a lot of other freeways increased by 20 to 30 percent, and congestion coming up from Federal Way and Tacoma started before 5 a.m.," said Jonathan Hopkins of Commute Seattle.
"So the peak gets busier, it spreads, it's going to be key that everyone does what they can to take action during that three-week period," Hopkins said.
Commute Seattle is offering free assistance for employers to plan for SR99 closure.
Hopkins urges people to telecommute or shift their work hours when possible.
Transit is increasingly popular for downtown workers, but during the 2016 closure, King County Metro reports a drop in riders by five to nine percent.
"I believe that the number of people coming downtown period dropped during that time," said Bill Bryant, managing director of Service Development at King County Metro.
Bright spots for transit in 2016 were light rail and Sounder commuter rail service, which saw ridership rise between 5 and 10 percent.
Most remarkable was ridership on King County's West Seattle water taxi, which surged 135 percent, and took many people who otherwise ride buses.
The 2016 numbers help show the impact losing SR99 has region-wide, but there are key differences between 2016 and 2019.
In 2016, a lot of people took a few days off during the nine-day closure.
The 2019 closure will be much longer.
"Very few people would be able to take vacation during a three to six week period," Bryant said. "That's one reason we're looking at this as a bigger challenge than 2016."
Another difference is more people are working downtown now than in 2016.
And buses that people might look to for relief, now run full on any normal day.
"We're inviting people to try the system at the same time we're really asking for patience from our riders," Bryant said.
King County Metro plans to add standby buses to go where they're needed.
Bus routes between stops will also be flexible to get around traffic as much as possible.
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