It's too narrow, the hillside is cut too steep, and traffic tends to be erratic. It's not safe in any way to put a bike lane on 28.

My geology professor in college remarked on the insane steepness of the hillside along 28 and how some of his colleagues refuse to drive on it due to this. That hillside is not naturally formed, it was cut with machinery in the 1920s, highway construction inspection on federal aid projects wasn't a thing til 1979. I wouldn't want a bike lane installed near it.