It was the creation, not of government, but of a loose affiliation of auto clubs in Oregon, Washington and British Columbia. The group chose an official north-south route and placed signs along the way identifying it as the Pacific Highway. Outside of major cities, the road was rough and unpaved but navigable. Following is a photo taken in 1915 of the route's grand opening along a stretch of highway that was plank paved near Seattle.
http://www.blackdiamondnow.net/black-diamond-now/2015/11/pacific-highway-circa-1915.html
