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 pick-up and loading of materials in any place marked as a freight curb loading zone during hours when the provisions applicable to these zones are in effect. In no case shall the stop for loading and unloading of materials exceed 30 minutes.
('75 Code, § 42.22) Penalty, see § 73.99