In terms of traffic signals by police officers, when is proceeding allowed?

Proceeding when parallel to the officer's arms is the correct answer because it indicates a specific instruction from the officer that allows drivers to move safely through an intersection or area, regardless of the standard traffic signals. Police officers may direct traffic in situations where normal signal operations are disrupted or where additional guidance is needed for safety reasons. The position of the officer's arms serves as a clear signal for drivers on how to proceed, ensuring that all vehicles are coordinated and that safety is prioritized.

The other options do not encompass the unique authority of a police officer in directing traffic. While safety and communication with other drivers are important in general driving situations, they do not apply to the specific context of following the commands of a police officer. Additionally, only proceeding when given a direct signal to go might suggest that waiting for verbal confirmation is necessary, which is not the case when observing the officer's physical signals.