Which of the following is classified as a "serious traffic violation" for CDL holders?

Driving under the influence of alcohol is classified as a "serious traffic violation" for CDL holders because it poses a significant risk to public safety and is a violation of federal regulations. CDL holders are held to higher standards of accountability due to the nature of their responsibilities, which often involve operating large commercial vehicles that can be more dangerous in the event of an accident. This violation can lead to severe penalties, including the suspension of a commercial driver's license and possible criminal charges, reflecting the serious nature of impaired driving.

Other options, while certainly traffic violations, do not carry the same level of severity in the context of CDL regulations. For instance, exceeding speed limits and running a red light could lead to points on the driving record but do not inherently indicate a risk to public safety at the same level as driving under the influence. Not wearing a seatbelt, while also important for personal safety, is typically treated as a lesser infraction compared to violations that involve alcohol or controlled substances.