“Motor carrier” is the registered owner, lessee, licensee, or bailee of any vehicle set forth in Section 34500, who operates or directs the operation of any such vehicle on either a for-hire or not-for-hire basis. “Motor carrier” also includes a motor carrier’s agents, officers, and representatives, as well as employees responsible for the hiring, supervising, training, assigning, or dispatching of drivers and employees concerned with the installation, inspection, and maintenance of motor vehicle equipment or accessories.