Why should a driver turn off the vehicle's retarder when the road is wet, icy, or snow-covered?
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Not quite.
Wrong. Retarder function is not limited to speeds above 55 mph; the concern with slippery roads is unrelated to any speed threshold.
The correct answer is B: The retarding power applied to the drive wheels can cause them to skid on a slippery surface.
49 CFR 383.111(a)(5) (Shifting)
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Correct!
Correct. Retarders apply additional braking power to the drive wheels only, and on a wet, icy, or snow-covered surface with poor traction, that extra retarding force can cause the drive wheels to skid. The manual instructs drivers to turn the retarder off in those conditions.
49 CFR 383.111(a)(5) (Shifting)
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Not quite.
Wrong. Retarders (exhaust, engine, hydraulic, or electric types) are separate systems from the air brake system and do not drain its air pressure reservoirs.
The correct answer is B: The retarding power applied to the drive wheels can cause them to skid on a slippery surface.
49 CFR 383.111(a)(5) (Shifting)
✗
Not quite.
Wrong. Retarders are legal and commonly used in normal driving conditions to reduce reliance on service brakes; the caution is specific to slippery road surfaces, not a blanket prohibition.
The correct answer is B: The retarding power applied to the drive wheels can cause them to skid on a slippery surface.