In the United States, orange is used for temporary traffic-control signs in work zones.
The orange background distinguishes temporary conditions from permanent warnings. Work-zone signs can warn drivers about road construction, maintenance operations, lane changes, detours, flaggers, or workers near the roadway. The color is specified in the Manual on Uniform Traffic Control Devices, commonly called the MUTCD.
Yellow remains the standard background for general warning signs, while fluorescent yellow-green is associated with especially important pedestrian, bicycle, and school-related warnings. Red is used mainly for stop, yield, and prohibition elements, and green commonly identifies directional or guide information.
Orange does not mean that every road project has identical rules. Drivers must also follow the wording, arrows, channelizing devices, temporary signals, and posted speed limits in the specific work zone. Work-zone layouts can change as construction progresses.