Final answer:
The minimum number of lanterns a subway track flagman should carry cannot be determined without more context or specific safety regulations.
Step-by-step explanation:
The minimum number of lanterns that a subway track flagman should carry cannot be determined from the information provided. Safety regulations regarding the equipment required for a flagman can vary based on the regulations of the specific transit authority, the country's safety laws, and the operational conditions of the work environment.
Therefore, to provide an accurate answer, additional information about the specific safety regulations or context would be necessary.