CDL Air Brakes TestUsing Air BrakesMedium
A commercial driver is operating a tractor-trailer on a long, steep downgrade. The vehicle is equipped with air brakes. To prevent brake fade and maintain control, which braking technique should the driver primarily employ?
- AEngaging the parking brake intermittently to assist the service brakes in slowing the vehicle.
- BUsing a low gear and applying the brakes lightly for extended periods to maintain a constant speed.
- CApplying the brakes firmly once at the top of the downgrade and releasing them only when reaching the bottom.
- DApplying the brakes hard enough to slow the vehicle by about 5 mph below a safe speed, then releasing until speed increases again.
Show answer & explanationAnswer & explanation
Correct answer: D. Applying the brakes hard enough to slow the vehicle by about 5 mph below a safe speed, then releasing until speed increases again.
The proper technique for braking on downgrades with air brakes is to use a 'snub braking' method. This involves applying the brakes hard enough to slow the vehicle below a safe speed, then releasing them to allow cooling, repeating as necessary.
Why the other options are wrong
- A. The parking brake is for parking only and should never be used to slow a moving vehicle, as it can cause loss of control and severe damage.
- B. Light, continuous braking can still cause brakes to overheat and fade, especially on long downgrades.
- C. This approach would lead to rapid brake fade as the brakes would overheat without periods to cool.
Snub Braking
A technique used on long downgrades to control vehicle speed and prevent brake fade by applying brakes firmly for short periods, then releasing them to cool.
- Prevents brake fade by allowing cooling.
- Used on long, steep downgrades.
- Involves firm, short brake applications.
Memory trick: Downhill, don't drag, just 'snub' to be safe.