How are one-way preferred routes depicted on an airway?

One-way preferred routes are depicted on airways using a bold arrow. This visual representation clearly indicates the direction of the flight along the route, helping pilots and air traffic controllers understand the intended flow of air traffic. The use of a bold arrow emphasizes that the route is not two-way—traffic is expected to follow it in one specified direction only, ensuring safety and efficiency in navigational practices. This distinction is particularly important in busy airspaces where multiple routes may be in close proximity, as it eliminates potential confusion regarding the path that an aircraft should follow.

The other options do not effectively convey the directional aspect of one-way preferred routes. For example, a solid line usually represents standard airways where traffic can flow in both directions, while dashed lines can indicate routes that may have restrictions. A color highlight may be used for various other navigational aids but doesn't specifically indicate the one-way nature of a route.