It's actually a bit interesting to see WSDOT's plan for i-5.
For capacity they aren't expanding I-5 directly, but expanding i-405 and sr167 instead for people trying to go past Seattle.
For i-5 within Seattle area, there are some 2030s plans to convert the hov lanes to toll lanes and reconfiguring the reversible express lane system.
* I-5 Managed Lanes: SR 16 to Pierce/ King County Line
* I-5 Managed Lanes: Pierce/ King County Line to I-405
* I-5 Managed Lanes: I-405 to US 2
For capacity they aren't expanding I-5 directly, but expanding i-405 and sr167 instead for people trying to go past Seattle.
For i-5 within Seattle area, there are some 2030s plans to convert the hov lanes to toll lanes and reconfiguring the reversible express lane system. * I-5 Managed Lanes: SR 16 to Pierce/ King County Line * I-5 Managed Lanes: Pierce/ King County Line to I-405 * I-5 Managed Lanes: I-405 to US 2
https://www.psrc.org/media/4840