Which type of gates is common to both O'Hare and Midway airports?

The correct answer is roll gates. Roll gates are commonly used at both O'Hare and Midway airports due to their practicality and space-saving design. These types of gates can efficiently open and close without taking up additional space, making them suitable for areas where room is limited, such as airport perimeters and access points. Roll gates offer a secure method for controlling access, providing both safety for airport operations and security for the areas they enclose.

Considering the other options, sliding gates typically require more operational space and are not as prevalent in airport environments where space efficiency is crucial. Security gates do play a vital role at airports, but the term is broad and can refer to various gate types, making them less specific to the commonality of O'Hare and Midway. Manual gates, while they do exist, are less efficient in high-traffic environments like airports, where automated or semi-automated solutions are preferred for quick access. Thus, roll gates are recognized for their effectiveness and common use at both airports.