Drunk driving regulations are strict in all cases, but they are even more so for people who hold commercial driver's licenses. Drivers who are at or above the legal drinking age have a blood alcohol concentration (BAC) limit of .08 percent, but the limit is much lower for commercial drivers.
The Federal Motor Carrier Safety Association (FMCSA) sets the standards for the BAC of commercial drivers, so states don't have free reign here. The limit for these drivers is .04 percent. This is a much lower limit than other drivers, but it is set this way for a good reason.
Commercial drivers are responsible for heavy loads of cargo, some of which is very sensitive. They transport everything from tanks of gasoline or milk to children or senior citizens. The size and weight of these vehicles also pose a risk to other drivers on the roads because they can cause serious crashes that lead to catastrophic injuries or death for innocent people.
Another rule that is set by the FMCSA is that these drivers can't operate any type of commercial vehicle within four hours of consuming alcohol. This is because of the way that the body is likely to metabolize the alcohol after the driver consumes the drinks.
A commercial driver who is stopped for a drinking and driving charge might end up losing their license. This is likely going to be devastating for the driver since it probably means he or she is going to lose their career. With this in mind, commercial drivers much fight these charges and take them seriously.
Source: FindLaw, "Commercial DUI Regulations," accessed Sep. 18, 2017