In the United States, what color are standard highway route markers in the Interstate system?

In the United States, standard Interstate Highway route markers are red, white, and blue.

The marker has a blue upper field, a red band near the top, and a white number and lettering. Its shield-like design identifies routes belonging to the Interstate Highway System, distinguishing them from many other American route-marker families.

The Interstate system was created by the Federal-Aid Highway Act of 1956 and developed into a nationwide network of controlled-access highways. Route numbers are generally even for east–west routes and odd for north–south routes, although geographic and historical exceptions exist.

These route markers should not be confused with guide signs. Large green signs provide destinations, exits, and distances, while the red-white-blue shield identifies the numbered Interstate route itself. The colors are therefore part of the route-marker identity, not a statement about the road’s speed limit or direction.