Huh. I use “highway” and “freeway” interchangeably. Just did a search and found the following, so thanks for enlightening me:

Highways have controlled areas, and traffic lights, tend to be placed in rural areas and always allow you to drive off. Freeways have higher speed limits and are, in essence, a faster way to get from one city to the other with minimal traffic control.

I guess maybe this is a result of my having grown up in a midwestern state where both could exist without distinction. TIL.