What is one key feature of the air brake system in trucks?

The air brake system in trucks is designed to function primarily using air pressure. This system operates by compressing air, which is then stored in tanks and used to create the force needed to engage the brakes. When the driver applies the brake pedal, the compressed air is released, activating the brakes to slow down or stop the vehicle.

This reliance on air pressure is crucial because it allows for greater braking power and control, especially in larger vehicles like trucks that require more force to achieve effective stopping distances. Furthermore, air brakes are designed to be fail-safe; if a loss of air pressure occurs, the brakes can engage automatically to prevent the vehicle from rolling.

Other systems mentioned, such as those that operate solely on electricity or use hydraulic pressure, either do not apply to trucks or serve different types of vehicles. Additionally, a manual force-only system would not provide the necessary power to safely and effectively brake a large truck. Thus, the correct answer emphasizes the essential role of air pressure in the operation and effectiveness of truck air brake systems.