How can you tell if a vehicle is equipped with air brakes?

A vehicle is equipped with air brakes if it features a red knob and a gauge that indicates air pressure. This is a specific characteristic of air brake systems, which use compressed air to operate the brakes. The red knob is typically used to engage or disengage the parking brake, while the air pressure gauge provides crucial information about the current pressure levels in the braking system. Consistent and adequate air pressure is essential for the brakes to function correctly, which is why monitoring it is vital for safety.

The presence of a red knob and gauge specifically signals drivers and operators about the functionality of the air brake system, making it a clear identifying feature. Other options, while they may provide clues about vehicle type or condition, do not directly indicate the presence of air brakes. For example, a standard gear shift is not unique to vehicles with air brakes, a loud hissing sound could occur for various reasons and is not a definitive indicator, and while larger vehicles often have air brakes, this is not a rule since not all large vehicles are equipped with them. Thus, the correct identification relies heavily on the gauges and knobs associated with the air brake system.