As it is today, I would never consider this route due to narrow shoulders and heavy traffic. But help is on the way. Here is a BikePortland article about a very exciting development. 

https://bikeportland.org/2021/07/28/oregon-has-a-new-plan-for-the-legendary-coast-bike-route-335702/amp

Al and I rode most of the Oregon coast in about 1989.  We drove to Portland and took the bus with our bikes to Necanium or thereabouts and rode to Crescent City, just over the state line into California, then bussed back to Portland as we only had a week.  We went in early September for cooler weather and fewer people on the road.

I don't remember the highway being particularly scary except for the beautiful McCullough bridges, which I chose to walk.  That was Oregon.  The highway had a 3-foot shoulder as I recall, which we considered decent back then.  I don't think we'd ever experienced anything better than that at the time.

But then we came to California and the shoulder disappeared altogether.  We were so freaked out by the time we got to Crescent City that we just went to a motel and hung out there for the rest of the day.  So much for my dream of seeing the redwood forest.  I've still never seen one.

Someday I'll ride down as far as Big Sur.  Someday.

In recent years ODOT has resurfaced 101 but not all the way to the edge of the existing asphalt layer, essentially narrowing the shoulder and making the edge dangerously abrupt. The increase in traffic since 1989 is also significant, with many road users driving rental RVs that they struggle to maintain in their lane. It’s a shame because it is a gorgeous route with wonderful state-run  $5 hiker/biker campgrounds along the way. I hope this new plan can make it as enjoyable as you found it back in the day. And I also hope you can get to the redwoods one way or another. 

Most of the Oregon coast route has far too much traffic for my tastes. No amount of road upgrades can fix that.

My very brief glance at the upgrades to this route seems to show mostly diversions off of 101 onto smaller side roads but there are only so many of those available. I think you are probably right, Wayne. Traffic is formidable and not worth my time or safety. 

I hate it when highway authorities do that!

But maybe I'm spoiled now.  That trip down the Oregon coast was before my first experience of cycle touring in Europe in 1992.  Now anything local just doesn't cut it in comparison.

Hi Jacquie! I rode the Three Capes Scenic route in 1996, in the third riding day of my first cross usa tour.  Here is what I wrote about it: " I thought this was the most spectacular stretch of road on the Oregon Coast. Nice. I stopped for the night at Cannon Beach. 75 miles on the bike with lots of climbing - I'd estimate it at least half a mile - and really great scenery"

I' ve done many tens of thousands of  kilometers touring in Europe and I don't think  I've seen a prettier beach although some of the beaches on the western coast of the  Adriatic are even more spectacular.