Out here, we can consider a highway any road with two lanes. Shoulder's aren't necessary nor is division. Divided roads and/or roads with shoulders are often rare in the mountains.

But... there's also many arterial roads that are marked as State or US highways. Many times, these go through a central business district and are marked with low speeds.

We also have suburban high speed arterial roads that are marked as highways and those that aren't. Those I consider the least safe. They usually combine heavy traffic, high speeds and high numbers of intersections. Unfortunately, cycling on them is often a necessity to get to where I need to go.

I used to have to ride on a 45mph, six lane suburban arterial to get to work. I never had more close call than when I rode on that road. It was not marked as a highway.