How are interstate route markers on a highway identified?

Answer: B — using a red and white sign

Interstate route markers on highways are identified using a red, white, and blue sign design. The shape of the sign is a shield, which is a distinctive feature that makes it easily recognizable for drivers. The red and white colors help to ensure visibility and differentiate interstate highways from other types of roads. This uniformity in color and design is crucial for guiding drivers effectively across state lines, indicating that they are on a federally designated highway that typically facilitates long-distance travel. The other options do not accurately reflect how interstate routes are marked. Numbers are indeed used on these signs to designate specific interstate highways, but the identification primarily revolves around the color scheme of the markers. Blue signs are generally reserved for services, such as gas, food, and lodging, while green signs are used for guide signs that indicate directions and distances to various locations, including exit signs on highways.