How do State and Federal Declarations of Emergency affect motor carrier operations?

When an official governmental Declaration of Emergency is issued for a type of major emergency, motor carriers and operators of commercial motor vehicles that are providing emergency relief through direct assistance to support State and local efforts to save lives or property or to protect public health or safety, are relieved from the Federal Motor Carrier Safety Regulations listed in 49 CFR Parts 390-399.  (The italicized words are defined in 49 CFR 390.5.) 

Even though safety regulations may be suspended, drivers and carriers are expected to use good judgment and not to operate vehicles when drivers are fatigued or ill, or under any conditions presenting a clear hazard to other motorists using the highways.