For what operations should the arrow board be used in the "caution" mode?

The correct answer focuses on the appropriate use of an arrow board in scenarios that warrant caution due to potentially hazardous conditions. When the arrow board is set to "caution" mode, it indicates to drivers that they should proceed with care and be prepared for changes in the roadway situation.

In the case of shoulder work or temporarily closing one lane, the arrow board effectively communicates to motorists that they should be alert to the possibility of encountering workers or equipment on the shoulder, and that lane changes or merging may be necessary. This mode helps to ensure smooth traffic flow while still emphasizing the need for drivers to pay attention to their surroundings and adjust their speed accordingly.

Other scenarios—that might involve directing traffic into one lane, general road construction, or flagging operations—often require more specific signals or directives that might not align with the cautionary role of the arrow board. For example, directing traffic into one lane usually necessitates a clear, specific instruction rather than a general caution, while flagging operations typically rely more on human traffic controllers to manage vehicle flows effectively.