No conveyance of any kind shall be permitted to be parked in any loading and unloading zone solely for the purpose of discharging or taking on passengers or persons. Whenever a conveyance of any kind is lawfully parked in a loading and unloading zone, it shall not be necessary for any such conveyance to be actually attended by one or more attendants, but the business of loading and unloading shall be carried on expediously and in a practical manner. (Code 1953, § 10.100)