Per the AAMVA CDL Manual, when a standee line is marked by a painted line on the floor, how wide must that line be?

49 CFR 383.117(a)(6) (operating practices not otherwise specified); AAMVA CDL Manual Section 4.2.3 "Standee Line," p. 4-2

A faded or improperly-sized standee line is harder for riders to notice, which defeats its safety purpose. This is the kind of specific number the exam uses to separate applicants who read the manual closely from those who only skimmed the general concept.