North Carolina CDL Air Brakes Practice Test

The spring brakes on a straight truck are designed to engage automatically when the air pressure drops to a certain level, thereby stopping the vehicle safely. Typically, this engagement occurs at around 20 PSI. This system serves as a safety feature to ensure that if there is a significant loss of air pressure in the braking system, the vehicle will still have a means of stopping, using the spring brakes to bring it to a halt. The choice of 20 PSI as the pressure at which the spring brakes activate reflects industry standards that prioritize safety. It is essential for commercial drivers to be aware of this threshold to manage their vehicle's air pressure effectively and ensure proper functioning of the braking system. Understanding this helps drivers identify potential air system failures early and take appropriate action to maintain safety on the road.