driving large trucks and buses require a commercial driver's license (cdl) to operate. obtaining a cdl requires extra education and training dealing with the special knowledge requirements and handling characteristics of such a large vehicle. drivers of commercial motor vehicles (cmvs) must adhere to the hours of service, which are regulations governing the driving hours of commercial drivers. these and all other rules regarding the safety of interstate commercial driving are issued by the federal motor carrier safety administration (fmcsa). the fmcsa is a division of the united states department of transportation (usdot), which governs all transportation-related industries such as trucking, shipping, railroads, and airlines. some other issues are handled by another branch of the usdot, the federal highway administration (fhwa).