When is it appropriate to use temporary traffic signals in a work zone?

Using temporary traffic signals in a work zone is appropriate when manual traffic control is not feasible or safe. In various scenarios, manually directing traffic can lead to unsafe conditions for both traffic control personnel and drivers. For example, if a work zone is located on a busy road where visibility is limited or traffic volume is high, using a traffic signal allows for efficient and safe management of vehicle flow. Additionally, temporary signals can maintain traffic progression, reduce confusion, and minimize delays without requiring constant human intervention, which could introduce inconsistencies or risks.

The other options do not align with safe practices for traffic management in work zones. Utilizing temporary signals after all work is completed or when the work zone is inactive does not make operational sense, as there would be no need for traffic control in a non-active scenario. Additionally, the absence of vehicles does not warrant the use of traffic signals, as their primary purpose is to manage traffic flow rather than to be operational in a void situation.