What is one factor that does NOT contribute to the requirement of hand brakes on cars?

The type of train crew present does not influence the requirement for hand brakes on cars. Hand brakes are primarily utilized to secure cars when they are stationary, regardless of who is operating the train or how experienced the crew may be.

In contrast, factors such as the grade of the track, the number of loads and empties, and weather conditions directly impact the effectiveness of a car's braking system and the potential for movement. For example, steeper grades may require additional hand brakes to prevent rolling, while the weight difference between loaded and empty cars could influence how they are secured. Weather conditions, such as rain or ice, can also play a significant role in traction and stability, necessitating the use of hand brakes to ensure safety. Thus, crew experience does not dictate the mechanical requirements for hand brake application.