Roadway signs in the United States increasingly use symbols rather than words to convey their message. Symbols provide instant communication with roadway users, overcome language barriers, and are becoming standard for traffic control devices throughout the world. Familiarity with symbols on traffic signs is important for every road user in order to maintain the safety and efficiency of our transportation facilities.
The color of roadway signs is an important indicator of the information they contain. The use of red on signs is limited to stop, yield, and prohibition signs. A white background indicates a regulatory sign; yellow conveys a general warning message; green shows permitted traffic movements or directional guidance; fluorescent yellow/green indicates pedestrian crossings and school zones; orange is used for warning and guidance in roadway work zones; coral is used for incident management signs;** blue indicates road user services, tourist information, and evacuation routes; and brown is for guidance to sites of public recreation or cultural interest.
Sign shape can also alert roadway users to the type of information displayed on a sign. Traffic regulations are conveyed in signs that are rectangular with the longer direction vertical or square. Additional regulatory signs are octagons for stop and inverted triangles for yield. Diamond-shaped signs signify warnings. Rectangular signs with the longer direction horizontal provide guidance information. Pentagons indicate school zones. A circular sign warns of a railroad crossing.
The illustration below shows how the shape and color of a sign indicate the nature of the message.