And given that Oregon was never able to push through an I-84 extension to Astoria, there are no Interstates that reach the actual Pacific Coast north of San Francisco.
Is there enough traffic west of Portland for a full interstate extension to the Pacific Ocean. I know US 26 is a freeway from Portland to a point west of Hillsboro, but beyond that, you’re out of the Portland metro area.
On the weekends during the summer? Yes.
The entire Oregon and Washington coast don't have any freeways to get inland.
This. Given that the Interstates were envisioned as a national defense system, it seems short sighted to not have them reach the coast north of San Francisco (and arguably, they don't reach north of LA), if for no other reason than to provide a means of evacuation in the event of Tsunami or other costal disaster, or to allow the movement of defense forces if someone get a wild hair and wants to invade the Pacific coast. And with the elimination of the costal railroads, there isn't even alternative means of moving goods to and from, or along the coast.
Washington has at least been trying with their upgrades to US 12, and Oregon has the right-of-way and bridges build for expansing OR 18 (among others), but a actual numbered interstate to the coast in both states would good for those reasons. Of course, I would also love to see both states work together to expand the Cascades system to cover the coasts and the inland communities, but that is also a pie-in-the-sky idea.