CDL General Knowledge TestDriving SafelyMedium
You are driving a heavy commercial vehicle down a long, steep downgrade. Which of the following is the most effective braking technique to maintain a safe speed and prevent brake fade?
- AShift to a lower gear and use the engine's braking power, supplementing with short, firm brake applications.
- BEngage the parking brake periodically to assist in slowing the vehicle.
- CApply the brakes lightly and continuously to keep speed in check.
- DDisengage the clutch and coast, using the foot brake only when necessary to slow down.
Show answer & explanationAnswer & explanation
Correct answer: A. Shift to a lower gear and use the engine's braking power, supplementing with short, firm brake applications.
The 'stab braking' or 'controlled braking' technique on downgrades involves using a low gear to maximize engine braking, supplemented by short, firm brake applications to control speed. This prevents continuous brake use that leads to overheating and fade.
Why the other options are wrong
- B. The parking brake is for parking, not for slowing a moving vehicle, and can cause loss of control or severe damage.
- C. Light, continuous braking causes excessive heat buildup and leads to brake fade.
- D. Coasting removes engine braking, placing full reliance on the service brakes, which will quickly overheat and fail.
Safe Downhill Braking
To safely descend a long, steep grade, drivers should select a low gear before starting the descent and use a 'controlled braking' technique to manage speed.
- Use a gear that keeps engine RPMs high enough for effective engine braking.
- Apply brakes firmly for a few seconds, then release for a few seconds.
- This allows brakes to cool between applications, preventing fade.
- Never coast or ride the brakes continuously.
Memory trick: Gear low, brakes slow, don't let the heat show!