What factor primarily influences the runway in use and the direction of arrivals and departures?

The primary factor influencing the runway in use and the direction of arrivals and departures is wind conditions. When determining which runway to use, air traffic controllers prioritize the runway orientation in relation to the wind direction. Aircraft are designed to take off and land into the wind to ensure better lift, control, and overall safety. This means that if the wind is blowing predominantly from a certain direction, the runways aligned with that wind direction will typically be used for arrivals and departures.

Though air traffic volume can influence operational decisions, it is secondary to wind conditions because safety and performance depend most critically on the aircraft's interaction with the wind. Aircraft weight does play a role in landing and takeoff distances but does not dictate the choice of runway. Weather patterns can affect visibility and other factors, but they typically do not have as direct an impact on runway selection as wind conditions do. Overall, the preference for aligning arrivals and departures with the wind is a fundamental practice in aviation safety.