Final answer:
Subway cars must be heated between 40 and 65 degrees Fahrenheit in winter to ensure passenger comfort and safety, preventing risks such as hypothermia while avoiding overheating.
Step-by-step explanation:
The requirement that subway cars in passenger service be kept heated between 40 and 65 degrees Fahrenheit during the winter season is most likely because these temperatures ensure the comfort and safety of passengers. The lower limit of 40 degrees prevents the interior of the cars from becoming too cold, which could lead to discomfort or health risks such as hypothermia. The upper limit of 65 degrees is set to provide a warm enough environment while avoiding overheating, which could also cause discomfort or health issues.