What is true about convex mirrors on a commercial motor vehicle, compared to flat (plane) mirrors?

49 CFR 383.111(a)(7); AAMVA CDL Manual Section 2.4.2, p.2-11, Fig 2.7

Misjudging distance in a convex mirror, thinking a vehicle is farther back than it actually is, is a common cause of unsafe lane changes and merges. Knowing that convex mirrors shrink objects and make them look farther away lets a driver compensate with extra following distance before trusting what the mirror shows. This distortion effect is a frequently tested detail on the knowledge exam.