Mapbox has significantly expanded its highway shield icon library to enhance map navigation by introducing 121 new icons that reflect the unique and complex designs of U.S. highway shields. These icons are crafted to improve turn-by-turn navigation by making it easier for users to associate maneuvers with recognizable road landmarks, featuring a consistent flat design for better legibility. Users can customize the icons' aesthetics in Mapbox Studio by adjusting color schemes and scaling them for smaller screens using the "Navigation" style in the Road Network component, which is particularly beneficial for in-car devices.