Officers of the Police Department and such officers as are assigned by the Chief of Police are hereby authorized to direct all traffic by voice, hand, audible or other signal in conformance with traffic laws, except that in the event of a fire or other emergency or to expedite traffic or to safeguard pedestrians, officers of the Police Department or members of the Fire Department may direct traffic as conditions may require, notwithstanding the provisions to the contrary contained in this chapter or the Vehicle Code.