No person shall park any commercial vehicle, as defined in the Vehicle Code, weighing more than six thousand pounds, nor unladen or laden vehicles, including campers, weighing more than six thousand pounds, and no person shall park a cement mixer, compressor or trailer on any street in a residential zone for more than two hours at any one time, except for:
A. Necessary loading and unloading;
B. Vehicles engaged in performing a service activity on the adjacent lot or parcel of land;
C. Vehicles used in conjunction with a lawful commercial use on the adjacent lot or parcel of land;
D. Vehicles used during the construction of buildings or structures on the adjacent lot or parcel of land;
E. Vehicles engaged in construction or maintenance within the street, alley, parkway or highway. (Prior code § 12-17)