Individual states have taken steps to legalize medical and even recreational use of marijuana in recent years. While the states have the right to make these decisions, commercial drivers, pilots and operators are still bound by federal regulations concerning safe operation of buses, trains, planes and trucks. Truck drivers are still in violation of these rules if they have any marijuana in their systems while operating their vehicles. This is an important consideration for the victims of truck accidents as state laws establishing safe limits for THC in the blood could be used to deny liability. Regardless of the state where the accident occurs, if the driver has THC levels higher than zero, he or she is in violation of Department of Transportation guidelines for commercial drivers.
The DOT released a policy notice, specifically informing truckers and trucking companies that state laws will not trump the current federal Drug and Alcohol Testing regulations. The issue likely arose as Colorado is considering a bill to set new rules regarding driving under the influence and marijuana. It is considering a limit of 5 nanograms per mL of blood.
Under federal rules, THC is a Schedule I drug. If a driver tests positive for marijuana, that driver must undergo a specific return-to-duty process, consisting of an interview, an education program and further drug testing. The driver cannot operate a commercial vehicle until that process is complete. While the driver may be allowed to use marijuana according to state law, he or she cannot operate a commercial vehicle while any THC remains in the bloodstream.
Source: Land Line, "Trucking regs trump state laws on marijuana use," by David Tanner, 4 April 2013