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General Knowledge · Seeing

Why should a driver check mirrors regularly throughout a trip, not only at the moment of a lane change or turn?

1.Regular checks build a picture of where other vehicles are located relative to the blind spotCorrect answer
2.It is required every single time the vehicle's own road speed changes by more than about 5 mph
3.It resets the mirrors' auto-dimming feature once it has been triggered by bright headlights from behind the vehicle
4.It prevents the mirrors from fogging up during cold weather or sudden changes in the outside humidity level

Explanation

A driver should check mirrors regularly throughout a trip, not only at the moment of a lane change or turn, because regular checks build an ongoing picture of where other vehicles are, including traffic that may be moving into a blind spot the mirrors cannot show directly. Use of mirrors is part of the required knowledge CDL applicants must have under 49 CFR 383.111(a)(7)(ii), but that paragraph only names it as a required knowledge topic; it does not itself set a specific mirror-check schedule, which is standard driver-training guidance rather than a codified federal rule. There is no federal speed threshold that triggers a mirror check, and mirror checks have nothing to do with auto-dimming or fogging, which are unrelated mirror features.

Source: 49 CFR 383.111(a)(7)(ii)

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