The Chief of Police shall be authorized to assign to any Cadet or Public Service Aide, by written delegation, the power and duty to enforce all street traffic laws of the County and all of the vehicle laws of the State of Maryland applicable to traffic in the County. Cadets and Public Service Aides so assigned by the Chief of Police are hereby authorized to direct all traffic by voice, hand, or signal in conformance with traffic laws; provided that, in the event of a fire or other emergency, or to expedite traffic, or to safeguard pedestrians, Cadets and Public Service Aides may direct traffic as conditions may require notwithstanding the provisions of the traffic laws; but subject, however, to limitations as established by the Chief of Police. Any Cadet or Public Service Aide acting in any of the capacities authorized under this Section shall be presumed to have been authorized to act in such capacities by the Chief of Police, unless there is direct testimony to the contrary.