General Knowledge · Controlling Speed

Under 49 CFR 392.14, what must a driver do when fog reduces visibility of the road ahead?

1.Reduce speed, since the regulation names fog among the conditions that require slowing down when they adversely affect visibilityCorrect answer

2.Turn on hazard flashers in place of slowing down, since flashers are treated as a full substitute for an actual speed reduction in fog

3.Maintain the current speed but check mirrors more often than usual, since the added danger is assumed to be only to the rear

4.Speed up briefly in order to clear the foggy area sooner, then resume the normal posted speed on the other side

Explanation

When fog reduces visibility, 49 CFR 392.14 requires a driver to reduce speed, since the regulation lists fog by name among the conditions that adversely affect visibility or traction and states that speed shall be reduced when such conditions exist. This is a genuine, directly codified rule; the broader driving principle behind it, keeping speed low enough to stop inside the distance the driver can actually see ahead, is required knowledge under 49 CFR 383.111(a)(9)(iv), though that paragraph itself only names "speed and visibility" as a topic, without stating the specific fog rule. The other options fail for a shared reason: each proposes a response, warning other drivers, watching a different direction, or speeding up, that does not shorten the driver's own stopping distance the way slowing down does.

Source: 49 CFR 392.14

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Under 49 CFR 392.14, what must a driver do when fog reduces visibility of the road ahead?

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