Final answer:
Airlines maintain safe distances and altitude separations regulated by the FAA to prevent collisions, and efficiencies such as the hub-and-spoke system have increased passenger volume while maintaining safety.
Step-by-step explanation:
Planes are able to fly without running into each other because of stringent regulations and flight control laws enforced by the Federal Aviation Administration (FAA). According to these regulations, a commercial airplane must maintain a buffer of five miles from another plane at the same altitude and adhere to a vertical separation of 2,000 feet when above or below another aircraft, which reduces to 1,000 feet if flying below 29,000 feet. Quantum mechanics provide an interesting analogy, suggesting that just as electrons occupy certain quantized positions, airplanes are also restricted to particular 'slots' in the sky to avoid collisions.
To increase efficiency, airlines have moved towards a hub-and-spoke system, concentrating flights at central hub cities and then dispersing to various spokes. This change, coupled with the competition following industry deregulation, has enabled airlines to fill more seats per flight, doubling the number of air passengers and creating more jobs within the industry, all while maintaining safety with the assistance of government safety inspectors. These developments have allowed air travel to steadily grow safer and more accessible over time