No person shall park a vehicle in violation of any prohibition or restriction when public notice thereof shall be duly indicated by official sign or signs executed as provided in section 6-2-1 of this chapter. Provided, that nothing herein shall be construed as prohibiting a vehicle from standing in an area prohibited or restricted pursuant to the provision of section 6-2-1 of this chapter for such period of time as is necessary for the reason of expeditious loading or unloading passengers, provided such loading or unloading shall not consume more than three (3) minutes, nor to prohibit or restrict any commercial vehicle from standing in any such area for such period of time as is necessary for reasonable expeditious loading, unloading and delivery or pick up of goods, merchandise, articles or materials, provided such loading, unloading and delivery or pick up shall not consume more than thirty (30) minutes. Neither shall any such prohibition or restriction be construed to apply to any ambulance, police, utility or emergency vehicle while the operator thereof is engaged in the necessary performance of emergency or police duties, nor shall it be construed to prohibit any vehicle from being brought to a stop to avoid collision or standing in compliance with the order of any public officer or the direction of any traffic control signal. (1990 Code § 12.302)