Interstate highways are a bit confusing in Hawaii since you aren’t actually moving between different states. However, there are important reasons why. Hawaii has interstate highways primarily to facilitate the speed of shipping and commerce, as well as maintaining the ability to move military units and vehicles in the event or threat of an invasion from a foreign nation.
Hawaii has four interstates—H1, H2, H3, and H201—which are all located on the island of Oahu. Although Oahu is not the largest island, it’s home to about a third of the state’s population and the capital, which means that it also has the heaviest traffic. With four interstates, drivers can move freely and quickly around the island— ideal for commerce and commuting.