A route or schedule of a motor vehicle for which a motor carrier permit is granted may not be changed or abandoned without written permission from the Commission. The Commission may only grant permission under paragraph (1) of this subsection if the Commission finds that the public welfare and convenience are not prejudiced by the change. Notwithstanding paragraph (1) of this subsection, the holder of a motor carrier permit may temporarily operate substitute or reserve vehicles, when necessary in an emergency, to maintain the required schedules over the holder’s route. This subtitle does not limit the power of a municipal corporation to adopt reasonable traffic regulations, including the power to: designate streets; and prohibit the use of certain streets or the parking of vehicles on those streets if the use or parking may threaten public safety or unduly congest traffic.