Commercial Driver’s License (CDL) Practice Exam

The legal and standard method for trucks and buses to hold their parking or emergency brakes is through air pressure. This is particularly true for vehicles equipped with air brakes, which are common in large trucks and buses. When engaged, the air pressure in the brake system acts to apply the brakes, holding the vehicle stationary.

Air brakes function by using compressed air to activate the brake mechanism, ensuring reliability and effectiveness in a range of driving conditions. This method is preferred and legally recognized as it is designed to provide a strong and secure means of preventing vehicles from rolling, especially in situations where a vehicle is parked on an incline. Air pressure systems allow for immediate engagement of the brakes and automatic release upon starting the vehicle, ensuring both safety and efficiency.

While mechanical locks, hydraulic pressure, and electric current can also be involved in various braking systems, they are not the primary legal means by which heavy-duty vehicles like trucks and buses secure their parking or emergency braking systems. Therefore, the reliance on air pressure is not only standard practice but also aligns with regulatory requirements for ensuring that heavy vehicles can safely hold their position.