No person shall stop, stand or park a vehicle for any purpose or period of time, other than for the expeditious loading or unloading of passengers or materials, in any place marked as a loading zone, during hours and days when the regulations applicable to the curb loading zone are effective, and then only for a period not to exceed three minutes for passengers or 20 minutes for materials.
(`81 Code, § 14-194) Penalty, see § 10.99