(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 or unloading of materials exceed thirty minutes.
(b) No person shall stop, for the purpose of loading or unloading in the Central Business District, any vehicle or combination of vehicles exceeding in length twenty-four feet, between the hours of 6:00 a.m. and 7:00 p.m. unless a permit therefor shall have been first obtained from the Chief of Police. This section shall not apply to buses.