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 Tennessee, it is indeed a criminal offense for a commercial vehicle operator to have a blood alcohol concentration (BAC) of .04 or higher, which is indeed half the BAC limit for drivers of non-commercial vehicles. For holders of a Commercial Driver's License (CDL), the stakes are particularly high as their livelihood often depends on maintaining their license. Under Tennessee law, a first-time DUI/DWI offense can result in a one-year suspension of the CDL. If a CDL holder commits a second DUI/DWI offense, they face the possibility of being permanently disqualified from holding a CDL. These regulations are designed to enforce stricter standards for commercial drivers and ensure public safety on the roads. The relevant laws can typically be found in the state's vehicle or transportation codes.