What is the primary purpose of STARs?

The primary purpose of Standard Terminal Arrival Routes (STARs) is to aid in transitioning to the approach procedure. STARs are designed to provide a standardized route for aircraft arriving at an airport, ensuring a smooth and efficient flow of air traffic. They help pilots and air traffic controllers manage the arrival phase of flight by providing clear path guidance from the enroute structure to the terminal area. By using STARs, aircraft can integrate more seamlessly into the approach to the airport, which enhances safety and reduces the potential for conflicting air traffic.

The other options refer to different aspects of flight operations. While facilitating landing under visual conditions is important, it pertains more closely to visual flight rules and standard approach procedures rather than the role of a STAR. Managing traffic congestion on the ground relates to surface management rather than the arrival phase of flight. Establishing takeoff procedures does not align with the function of STARs, as these routes are specifically designed for arrivals, not departures.