(a) Commercial. No person shall stop, stand or park a vehicle for any purpose or length of time other than for the expeditious unloading and delivery or pickup and loading of materials in any place marked as a commercial curb loading zone during hours when the provisions applicable to such zones are in effect. In no case shall the stop for loading and unloading of materials exceed thirty minutes.
(b) Passenger. No person shall stop, stand or park a vehicle for any purpose or period of time other than for the expeditious loading or unloading of passengers in any place marked as a passenger curb loading zone during hours when the provisions applicable to such curb loading zone are effective, and then only for a period not to exceed three minutes.