Bye, Viaduct
At 10pm tonight, the main segment of the viaduct closes forever. The Battery Street Tunnel (and the corresponding Western Ave. ramps) will remain open for another 3 weeks. It's part civic eyesore, part scenic drive, and part important piece of transit infrastructure. Seattle will never be the same.
The SR99 tunnel is not a replacement on any of those counts, but we won't even get that for three weeks. In the meantime, the car capacity of downtown plummets. Thanks to a lack of leadership for several years at many levels, transit will also suffer just as we ask it to do more in this entirely foreseeable ordeal.
The general advice is to stay away, but most transit service will continue to operate. Several new options may also help at the margins. And you still want to get around, so here's a guide to service from least to most hosed.
The West Seattle Water Taxi and its feeder routes are getting higher frequency.
Biking is unlikely to get slower, although the City's uneven interest in your safety remains. Generalized gridlock reduces unsafe auto speeds and will therefore make many bike rides more pleasant. There are some minor adjustments to bike paths around the viaduct.
Sound Transit rail is mostly immune to congestion. Link crowding will be a problem, as the agency bought barely enough railcars to handle a normal rushhour. There will be one additional train in reserve to relieve crowding. If station access usually keeps you off the train, in effect your transit fare now counts towards your Uber/Lyft/ReachNow fare if traveling to or from most Link stations. Regrettably, this promotion does not extend to parking-limited Sounder service that has additional capacity.
Metro in-city routes and streectars will suffer from the expected increase in general congestion because many of the area's key chokepoints lack dedicated bus lanes. In particular, most cars coming south on Aurora Ave. will get off at Denny and contend with core bus lines there. There will be one additional block of bus lane northbound, but E Line riders are forgiven for finding that inadequate. The taxi promotion also includes a few Metro hubs like Northgate.
Buses that use I-5 lack any sort of HOV or bus lane for significant stretches, especially north of downtown. I-5 will likely bear the brunt of diversion from SR99. WSDOT, never missing an opportunity to miss the point, is somehow temporarily removing HOV restrictions from a southbound segment between Mercer and Corson St., parts of which carries virtually all I-5 corridor buses.
However, it's buses that use the viaduct today that, obviously, will the bear the brunt of the changes. From the West Seattle Bridge, they will travel north on 4th Ave and south on 1st Avenue through Sodo, before ending up on 3rd through downtown, as before. A temporary bus lane will speed up the exit from Spokane St. onto 4th Avenue, but trips will be slower than the old route. OneBusAway will not reflect the new routes. The reroutes start at 8pm tonight, so savor your last trip above it all today.
The yellow routes are the relevant ones.