What shape are the route markers in the INTERSTATE SYSTEM?

Answer: D — Shield

The route markers in the Interstate System are shaped like a shield. This distinctive shield shape is designed to be easily recognizable and is used to denote the various interstate highways across the United States. The shield features a blue background with a red top and white lettering, making it highly visible to drivers. This design aids in quick identification, ensuring that travelers can navigate the interstate system efficiently and safely. The unique shape helps differentiate interstate routes from other road signs, such as those for state highways, which may use different shapes and designs.