VOR airways in a shared route system are combined based on what factor?

In a shared route system, VOR (VHF Omni-directional Range) airways are combined based on the route numbers of the airways that coincide. This methodology allows for streamlined navigation by utilizing the existing airways that overlap, which helps to facilitate aircraft movement and enhances efficiency in air traffic management. The primary goal is to optimize the routes taken by aircraft while maintaining safety standards.

When two or more VOR airways overlap, the combination of their route numbers provides an effective way to designate a single, usable route for pilots and air traffic controllers. This system minimizes confusion and ensures that all aircraft are utilizing the same route in shared airspace, ultimately leading to better coordination and reduced chances of conflict.

The other choices provide various geographic or numeric considerations that are not part of the official air traffic management policies for combining air routes. Therefore, focusing on the actual route numbers that coincide is the logical and established standard in this context.