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 Washington State, it is indeed a criminal offense for a commercial vehicle operator to have a blood alcohol concentration (BAC) of .04 or higher, as per RCW 46.25.090. This limit is indeed half the BAC limit of .08 that applies to drivers of non-commercial vehicles. For holders of a Commercial Driver's License (CDL), the consequences of a DUI (Driving Under the Influence) conviction can be severe, whether the offense occurs in a commercial or non-commercial vehicle. Upon a first DUI conviction, a CDL holder faces a one-year disqualification from operating a commercial vehicle. If the DUI involved transporting hazardous materials, the disqualification period extends to three years. A second DUI conviction results in a lifetime disqualification, which can 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.