What does brake lag refer to?

Brake lag specifically refers to the time it takes for air to travel through the brake lines and reach the brake actuators in an air brake system. When a driver engages the brake pedal, there is a slight delay while the compressed air flows from the air reservoir to the brake chambers to initiate braking. This delay means there is a small interval where the vehicle continues to travel forward before the brakes actually engage, which can be crucial in emergency stopping situations. Understanding brake lag helps drivers anticipate braking performance and adjust their driving accordingly, especially in larger vehicles where air brake systems are commonly used.

Other options focus on different aspects of braking. One mentions the distance traveled before brakes activate, which, while related to brake lag, does not specifically identify the time taken for air to reach the actuators. Another discusses the increase in stopping distance in wet conditions, which pertains to traction changes rather than the mechanical delay in brake activation. The last option speaks to the responsiveness of the brake system to driver inputs, which relates to overall brake performance rather than the specific phenomenon of brake lag.