Which of the following is defined as a 'serious traffic violation' that can lead to CDL disqualification if committed twice within three years?

49 CFR 383.51, Table 2 to Section 383.51 (serious traffic violations); AAMVA CDL Manual Sec. 1.3.3, p.1-9

The 15-mph threshold is a specific, testable number, not a vague 'speeding' rule. Drivers who don't know the exact definition can rack up disqualifying violations without realizing their CDL is at risk, since two serious violations in three years already triggers a 60-day loss of driving privileges.