The FMCSA announces a revision of the regulatory guidance concerning the applicability of the Federal Motor Carrier Safety Regulations (FMCSRs) to mobile cranes operated in interstate commerce. The regulatory guidance is presented in a question-and-answer format. The guidance is generally applicable to drivers, commercial motor vehicles (CMVs), and motor carrier operations subject to the FMCSRs. All prior interpretations and regulatory guidance concerning the applicability of the FMCSRs to operations of mobile cranes in interstate commerce issued in the Federal Register, as well as memoranda and letters, may no longer be relied upon as authoritative if they are inconsistent with the guidance published today. This guidance will provide the motor carrier industry and Federal, state, and local law enforcement officials with uniform information for assessing the applicability of the FMCSRs to the operation of mobile cranes.