Nothing in this title shall be construed to prevent the vehicles of the United States postal department, while engaged in the business of said department, or the duly authorized and licensed operators of such vehicles in pursuance of their duties under said department from:
A. Double parking such vehicles while engaged in collecting and delivering U.S. mail.
B. Leaving the vehicle while the motor is running in a double parked condition without a licensed operator therein.
C. Using areas designated as "loading zones" and "taxi zones" for the collection and delivery of the U.S. mail.
D. Leaving the vehicle parked in an alley where less than ten feet (10') of alley width remains for the use of through traffic.
E. The use of designated passenger loading zones, however, such exemptions shall apply only for the purpose of momentary stops for mail pick up and delivery, and shall not permit the use of such areas for the general mail delivery. (1986 Code § 20-78)