Final answer:
A low level air route is in controlled airspace, starting at 1,200 ft. (365 m) and going up to just below 18,000 ft. (5,500 m). These routes are within the troposphere, where commercial aviation primarily operates and is subject to FAA regulations.
Step-by-step explanation:
A low level air route is controlled airspace and extends from 1,200 ft. (365 m) up to but not including 18,000 ft. (5,500 m). This type of airspace is designed to accommodate air traffic under the control of air traffic control. The lower limit of 1,200 ft. (365 m) above the surface is above the general maximum elevation figure to provide a transition zone between the terminal control areas and the en-route environment, ensuring safety and efficiency in navigation and air traffic management.
The troposphere is the lowest layer of the atmosphere, extending from the Earth's surface to an altitude of about 11-13 km (7-8 miles). Most commercial aviation and weather phenomena occur within the troposphere. The Federal Aviation Administration regulates aircraft flight paths to ensure safety by prescribing minimum separation standards in both horizontal and vertical dimensions.