Air Brake Practice Test

What is considered the reason for the longer stopping time of air brakes compared to hydraulic brakes?

1. Use of heavier materials

2. Reaction distance

3. Brake lag

4. Driver reaction time

The correct answer is: Brake lag

The longer stopping time of air brakes is primarily due to brake lag. When the driver applies the brakes in a system that uses air brakes, there is a delay before the braking action is fully engaged. This lag occurs because air must travel through the system to reach the brake chambers, where it is then converted into mechanical action to apply the brakes. The pneumatic system inherently has a delay involved due to the time taken for air to build up pressure and activate the brake components. In comparison, hydraulic brakes operate more quickly because they use fluid that can be acted on more instantly without the need for compressing air. The quick transfer of pressure in hydraulic systems allows for more immediate response in braking, which reduces the overall stopping time. Other factors, such as reaction distance and driver reaction time, contribute to the overall stopping distance but do not directly relate to the inherent mechanical behavior of the braking systems themselves. While heavier materials in construction may contribute to the weight of the vehicle and subsequently impact stopping distance, they do not specifically account for the characteristics of air brake systems.