CDL General Knowledge TestDriving SafelyHard
What is the primary reason for a commercial driver to perform a 'controlled braking' maneuver (also known as stab braking) in an emergency stop with a non-ABS equipped vehicle?
- ATo engage the parking brake as a secondary stopping mechanism.
- BTo prevent wheel lock-up and maintain steering control.
- CTo quickly cool down overheated brake components.
- DTo activate the anti-lock braking system more effectively.
Show answer & explanationAnswer & explanation
Correct answer: B. To prevent wheel lock-up and maintain steering control.
Controlled braking (stab braking) involves applying the brakes fully until just before lock-up, then releasing and reapplying. This technique is used in non-ABS vehicles to prevent wheel lock-up, which causes skidding and loss of steering control.
Why the other options are wrong
- A. Engaging the parking brake during an emergency stop can cause wheel lock-up, especially on drive axles, leading to a dangerous skid or jackknife.
- C. While intermittent braking can help cool brakes, the primary purpose of controlled braking in an emergency is to maintain control.
- D. Controlled braking is for non-ABS vehicles; it does not activate or enhance ABS.
Controlled/Stab Braking (Non-ABS)
An emergency braking technique for vehicles without Anti-lock Braking Systems (ABS), where the brakes are applied firmly until just before lock-up, then released and reapplied.
- Apply brakes hard, then release when wheels are about to lock.
- Reapply brakes as soon as wheels roll again.
- Purpose is to maintain steering control by preventing full wheel lock-up.
- Different from ABS, which does this automatically.
Memory trick: Stab and release, steer with ease.