(a) 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 truck 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 30 minutes.
(b) No person shall cause any vehicle to stand upon any street for the purpose of receiving or unloading freight, where there is a public alley from which such freight can be delivered or received. No person shall cause any vehicle to stand on any highway so as to obstruct traffic in or through such highway, or to obstruct any coal chute on any highway.