There are definitely interstate highways in Hawaii. Though they don’t cross state lines, Hawaii’s interstates facilitate commerce and allow the military to move smoothly across the island in the event of an invasion.
Hawaii’s interstate highways are all on Oahu, including H1, H2, H3, and H201. Due to a population of almost 900,000 people on a small island, these interstates make travel possible and traffic a little less hectic.