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Difficulty: Very hardMountain Driving and Steep Downgrades

During a steep mountain descent on an ice-covered road, if a commercial vehicle features a fully functional Anti-lock Braking System (ABS) across all axles, the driver can safely rely on the engine retarder for speed control because the ABS will automatically manage traction and prevent drive-wheel skids.

Answer: Answer

Answer

False
The statement is false. According to commercial driving safety standards, engine retarders must always be turned off when driving on wet, icy, or snow-covered roads. The Anti-lock Braking System (ABS) modulates air pressure to the service brakes to prevent lockup, but it does not control the braking torque exerted by the engine retarder on the drive wheels. Allowing the retarder to operate on ice can easily cause the drive wheels to lose traction and initiate a skid.

Step-by-Step Solution

1
Analyze the driving conditions and the vehicle safety systems interacting in the scenario.
The scenario involves a steep mountain downgrade, an ice-covered road surface, an active engine retarder, and a functional Anti-lock Braking System (ABS).
Identifying the specific environmental hazards and mechanical systems is necessary to apply the correct commercial driving regulations.
2
Evaluate the operational scope of the Anti-lock Braking System (ABS) relative to auxiliary braking systems.
ABS modulates air pressure specifically to the service brakes to prevent wheel lockup during a brake application; it does not directly control or modulate the continuous braking torque applied by the engine retarder to the drive axles.
Understanding system limitations prevents dangerous overreliance on automated safety features during critical maneuvers.
3
Apply the FMCSA CDL manual rule for engine retarder usage in poor traction conditions.
The manual categorically mandates that engine retarders must be turned off whenever the road is wet, icy, or snow-covered to prevent drive-wheel skids, making no exceptions for ABS-equipped vehicles.
Retarders apply continuous mechanical drag which can easily break traction on slippery surfaces and lead to an uncontrollable jackknife, regardless of whether the service brakes have ABS protection.

Key Concept

Engine Retarder Limitations in Adverse Weather Conditions
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Topics

Mountain Driving and Steep Downgrades

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