score:5
A quick check of the segment explorer in Strava shows that many people frequently run on the trails between Tillamook Head and Indian Beach Trailhead, and they also frequently run the length of Ecola State Park Road. In fact it's popular with both runners and cyclists.
For the trail segment, do note that you will gain about 1,000 feet of elevation, and there are switchbacks/moderately rough terrain. Runners generally average 2-3 minutes/mile slower than their usual city-running average when running this particular route.
For the road segment, just stay on the left and wear something visible. People drive slowly.
Upvote:4
I successfully walked from Les Shirley Park all the way to Tillamook Head (through the Indian Beach Trail, then through the coastal part of the Clatsop Loop Trail, and through the Hikers Camp) this December. It was raining the day before my hike and earlier that week, and the trails were muddy and slippery, but nothing unpassable. I've only encountered a couple of cars on Ecola State Park Rd. (in the morning).