CDL Combination Vehicles TestDriving Combination Vehicles SafelyMedium
You are driving a combination vehicle with a fully loaded trailer on a steep downgrade. What is the primary reason for selecting a lower gear before starting the downgrade?
- ATo increase fuel efficiency by reducing engine RPMs.
- BTo prevent the service brakes from overheating and failing.
- CTo improve steering response during the descent.
- DTo allow for faster acceleration at the bottom of the hill.
Show answer & explanationAnswer & explanation
Correct answer: B. To prevent the service brakes from overheating and failing.
Using a lower gear (engine braking) helps control the vehicle's speed on a downgrade, reducing the need for constant application of the service brakes. This prevents the brakes from overheating, which can lead to brake fade or complete brake failure.
Why the other options are wrong
- A. Lower gears typically increase engine RPMs, which is not primarily for fuel efficiency but for engine braking power.
- C. Steering response is primarily affected by speed and road conditions, not directly by the chosen gear on a downgrade, though controlled speed contributes to better steering control.
- D. While a lower gear provides more torque, faster acceleration at the bottom of a hill is not the primary safety concern when starting a downgrade.
Downgrade Braking
Technique for controlling vehicle speed on steep descents using engine braking to prevent service brake overheating.
- Select a lower gear before starting the descent.
- Gear should be low enough to hold speed without continuous braking.
- Use service brakes sparingly for short, firm applications.
- Avoid riding the brakes.
Memory trick: Down a hill, low gear will thrill (your brakes, by saving them).