Welcome to OpenStreetMap! Road classification is a contentious topic, especially for high-importance roads like expressways. https://wiki.openstreetmap.org/wiki/Santa_Clara_County,_California#Expressways says Expressways should be tagged as highway=trunk. I encourage you to ask about it in the OSM forum https://community.openstreetmap.org/c/communities/us/78 or the OSMUS Slack https://slack.openstreetmap.us/ !