Emergency vehicles should be deployed as advance warning and blocking when which of the following activities is happening?

The correct choice highlights the need for emergency vehicles to be deployed as advance warning and blocking when temporary traffic control devices are being removed. This is crucial because the removal of these devices can create confusion and potential hazards for drivers. By having emergency vehicles in position, they serve to alert and guide traffic around the work area safely. This helps prevent further accidents and ensures the safety of both the personnel involved in the removal of the devices and the traveling public.

During activities like addressing a new incident, collecting evidence, or having witnesses provide statements, while there may be a need for safety measures, the approach to traffic management can differ. In those scenarios, the primary focus is often on investigation processes or managing ongoing incidents rather than on the specific need to redirect or control traffic flow that could arise during the removal of traffic control devices. Therefore, the deployment of emergency vehicles is more critical and directly relevant in the context of removing these temporary traffic measures, making choice B the most appropriate answer.