Black on orange signs on a highway identify:

Black on orange signs on a highway are specifically used to convey information related to work zones. This color combination is a standard across the United States and is crucial for ensuring driver awareness and safety in areas where construction, maintenance, or other activities affecting the roadway are taking place.

These signs may indicate a variety of instructions or warnings, such as reduced speed limits, detours, or other conditions that drivers should be aware of while navigating through work zones. The use of the orange color helps to signal caution and alerts drivers to be vigilant, as the work zone may have unique hazards or interruptions to normal traffic patterns. This designation is essential for maintaining safety for both drivers and construction workers.

In contrast, the other options relate to different types of signage or information, such as permanent traffic regulations or speed limits, which do not use the black on orange color scheme and do not pertain specifically to work zones. Hazardous materials signs have distinct colors and symbols to alert drivers about safety information related to transportation of dangerous goods, which is also separate from work zone notifications.