I agree that the “expressway=yes” criteria of having a high speed is met. However, I believe the primary disqualification here is the matter of access control of which there is very little along the whole segment except for maybe the section in Santa Cruz between Chestnut and River due to its median barrier.
The wiki for tagging “expressway=yes” includes the following graphic that says for undivided roads, “expressway=yes” should only be used in cases with “full access control”.
Given the very strict threshold of “full access control”, this makes me think the expressway tag should be set to “no” for nearly all of the highway between Santa Cruz and Pacifica.