Illinois CDL Practice Exam

Spring brakes are a crucial component in an air brake system, specifically designed to serve as both emergency and parking brakes. These brakes utilize powerful springs that automatically engage when air pressure drops to a certain level, ensuring that the vehicle comes to a stop when it's not actively being controlled by the driver.

The primary function of the spring brakes is safety. In the event of an air pressure failure, the springs will activate, bringing the vehicle to a halt. This is particularly important for large commercial vehicles where maintaining control is vital to prevent accidents. Additionally, when a vehicle is parked, the spring brakes automatically engage, preventing it from rolling away without the driver's supervision.

In contrast, spring brakes are not typically engaged during regular driving, acceleration, or deceleration, as those functions are managed by the service brakes, which provide the necessary control and stopping power while the vehicle is in motion.