When driving a commercial motor vehicle on a roadway covered with packed snow where the no… — Commercial Driver's License (CDL) General Knowledge Exam

When driving a commercial motor vehicle on a roadway covered with packed snow where the normal posted speed limit is $50\text{ mph}$ , which combination of speed reduction and auxiliary brake management is required?

A
Reduce speed by one-third to approximately $33\text{ mph}$ and keep the engine retarder active to assist vehicle braking.
Reduce speed to $25\text{ mph}$ or below and turn off the engine retarder completely.Answer
C
Reduce speed to $25\text{ mph}$ or below and set the engine retarder to maximum resistance to reduce wear on service brakes.
D
Maintain $50\text{ mph}$ on straight road sections and apply heavy service braking while steering through curves.

Answer

Reduce speed to

25\text{ mph}

or below and turn off the engine retarder completely.

According to commercial driving regulations, drivers must reduce their speed by one-half or more on packed snow (slowing from

50\text{ mph}

25\text{ mph}

or less). Additionally, engine retarders must always be switched off whenever road surfaces are slippery (wet, snowy, or icy) because retarder braking torque can cause the drive wheels to lose traction and trigger a dangerous drive-wheel skid or jackknife.

Step-by-Step Solution

Calculate the required speed reduction for packed snow.

Reduce speed by at least

1/2

, lowering the maximum speed from

50\text{ mph}

25\text{ mph}

or less.

Official commercial driving standards require reducing speed by at least one-half on packed snow to maintain adequate stopping distance and tire traction.

Determine the proper setting for auxiliary brakes and engine retarders.

Disengage and turn off the engine retarder.

When drive wheels have reduced traction due to snow, ice, or water, retarder braking force can easily lock the drive wheels and cause an immediate skid or jackknife.

Key Concept

Speed adjustment on packed snow and engine retarder safety on slippery surfaces

Estimated Time:1m 0s

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