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General Knowledge · Seeing

What should a driver keep in mind when using a convex ("fisheye") mirror to check for traffic to the side or rear?

1.Objects appear smaller and farther away in a convex mirror than they actually are, so the driver must mentally adjust for that distortionCorrect answer
2.Convex mirrors only work correctly once the vehicle's own speed is above roughly 40 mph out on the open highway
3.Convex mirrors eliminate every one of a vehicle's blind spots entirely, with no need for an actual shoulder check at all
4.Convex mirrors reverse left and right, so a vehicle appearing on the right side of the mirror is actually on the left

Explanation

A convex mirror shows a wider area than a flat mirror, but it also makes objects appear smaller and farther away than they actually are, so a driver has to account for that distortion rather than trusting the apparent distance at a glance. 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 describe how a convex mirror distorts distance, which is standard driver-training guidance rather than a codified federal rule. Convex mirrors work the same way at any speed and do not eliminate blind spots entirely, and they do not reverse left and right; a vehicle seen on the right side of a convex mirror is genuinely on the right.

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

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