What are the vertical dimensions of a low-level air route?

The vertical dimensions of a low-level air route extend from the surface to 17,999 feet above sea level (ASL). This designation is crucial for navigation and air traffic management, particularly for aircraft operating at lower altitudes. These routes are typically established to facilitate safe and efficient navigation for both general aviation and commercial flights at lower altitudes, which may involve avoiding obstacles like terrain and ensuring proper separation from higher altitude air traffic.

The choice correctly reflects this standard as prescribed by aviation authorities, ensuring pilots have clear guidelines for navigating low-level airspace. In contrast, lower altitudes such as surface to 15,000 feet ASL would restrict the routes available for navigation, and dimensions that start from 2,000 feet AGL or that are specified above 18,000 feet ASL represent different classifications of airspace that do not apply to low-level air routes.