SDOT is studying a replacement for the Ballard Bridge, the westernmost road crossing of the Lake Washington Ship Canal. The current bridge opened in 1917 (and gained new approaches in 1940), but does not meet modern safety and earthquake standards. It is also extremely hazardous to cross on foot or by bike, with tiny sidewalks compared to even its contemporaries from the era.
Project page: http://www.seattle.gov/transportation/projects-and-programs/programs/bridges-stairs-and-other-structures/bridges/ballard-bridge-planning-study
The actual replacement is not funded yet and may take decades of debate to actually happen, but there is at least a few proposals floating around. The October Final Report (http://www.seattle.gov/Documents/Departments/SDOT/BridgeStairsProgram/bridges/Ballard/BBPS_AlternativesComparisonReport_Final_withAppendices.pdf) (large PDF warning) has a few scenarios with various costs, and includes rebuilding the Nickerson/Emerson interchange on 15th Avenue West at the south end of the bridge.
The Low-Level Alternative ($330 to 710 million):
(https://i.imgur.com/X45Aoyz.jpg)
The Mid-Level Movable Alternative ($680 million to $1.4 billion):
(https://i.imgur.com/nJoBMPV.jpg)
The High-Level Fixed Alternative (cost estimate not included):
(https://i.imgur.com/PsaIYGk.jpg)
Sound Transit will be building a parallel crossing for the Ballard light rail line (originally scheduled to open in 2035, but with COVID fallout there s no firm date), which could be a parallel bridge or a tunnel.
(There is also a replacement study for the Magnolia Bridge, but that is a whole other can of worms)
Interesting. I'm surprised that they don't try to combine a Ballard Bridge replacement and the Sound Transit bridge into a unified structure. Might save on costs, and they could have some fun with it, like putting the rail underneath or doing a double-lift bridge, like the Steel Bridge, in Portland. Might cost a little more than a single bride, but certainly cheaper than two, both for construction and ROW acquisition.
My thought as well. One factor might be that one disaster could knock out both the motor vehicle/bicycle/pedestrian bridge and the light rail bridge, while if they were separate one might take a bus if the light rail bridge was out or take the light rail if the motor vehicle bridge was out.