In many states it is a criminal offense (DUI/DWI) to operate a commercial vehicle with a blood alcohol concentration of .04 or more—which is half of the BAC usually required to commit the DUI/DWI offense while driving a non-commercial vehicle. Because most holders of commercial driver’s licenses (CDLs) depend on their license to earn a living, the consequences of a DUI/DWI conviction for a CDL holder—including a conviction while operating a non-commercial vehicle—are serious.

Laws vary from state to state but a CDL holder’s license may be suspended for one year for the first offense, and with a second DUI/DWI conviction the CDL holder may be permanently disqualified from holding a CDL.

These laws are generally located in a state’s statutes—often in the vehicle code, motor vehicle code, or transportation code.

In South Carolina, it is indeed a criminal offense for a commercial vehicle operator to have a blood alcohol concentration (BAC) of .04 or more, which is consistent with federal regulations and is indeed half the BAC limit for non-commercial drivers, who are subject to a limit of .08. For holders of a Commercial Driver's License (CDL), the consequences of a DUI (Driving Under the Influence) conviction can be particularly severe. Under South Carolina law, a first offense DUI while operating a commercial vehicle can result in a one-year disqualification of the CDL. If the individual is transporting hazardous materials at the time, the disqualification period is three years. A second DUI conviction, regardless of whether it occurs in a commercial or non-commercial vehicle, can lead to a lifetime disqualification, which may be reduced to 10 years under certain conditions. These regulations are designed to ensure the safety of the roads and reflect the higher standards of conduct expected from professional drivers. The relevant laws can be found in the South Carolina Code of Laws, particularly in the sections dealing with motor vehicles and traffic regulations.