I guess there are two types of highways:

• freeways - no lights, and what I usually refer to when I say "highway"
• inter-city highway - pretty much like any other road, but there's a constant name between cities - usually get replaced by freeways, but keep the name (e.g. State Street in Utah, 516 in WA [272nd coming off I-18], etc)

My understanding is that most people don't refer to the second as a highway, they're just arterial roads most people in the area are familiar with.