How is airspace along airways or routes typically protected?

The correct choice indicates that airspace along airways or routes is protected by a buffer of 4 miles on either side of the centerline. This protective measure ensures that aircraft operating in and out of these airspaces maintain a safe distance from obstacles and other aircraft, providing a margin of safety for navigation and flight operations.

Airways are defined air routes that aircraft use for navigation, particularly under instrument flight rules (IFR). The 4-mile buffer on either side of the centerline is a standard measurement that accounts for the width of the airspace necessary to accommodate typical aircraft deviations to the left or right while flying along the designated route. This level of protection is crucial for air traffic management, as it helps to minimize the risk of mid-air collisions and ensures that there is adequate separation for aircraft in transit.

In a broader aviation context, understanding the dimensions of protected airspace allows pilots, air traffic controllers, and flight planners to maintain safe operations, especially in busy airspace where multiple aircraft may be operating simultaneously.