Which altitudes must aircraft assigned specific V routes (like V9, V555) operate at northbound and southbound?

In the context of V routes within the National Airspace System, the altitude assignments follow a systematic approach to ensure safe vertical separation between aircraft traveling in opposite directions. For aircraft assigned to specific V routes like V9 and V555, aircraft flying northbound typically operate at odd altitudes, while those flying southbound operate at even altitudes.

This methodology is important for maintaining organized air traffic and reducing the risk of potential mid-air collisions. By assigning odd altitudes to northbound traffic, it prevents overlap with southbound traffic, which is assigned even altitudes. This structured altitude separation is a fundamental aspect of air traffic control procedures, enhancing safety and efficiency in the handling of flights on these established routes.