No person shall stop, stand, or park a vehicle other than a bus in a bus stop, or other than a taxicab in a taxicab stand when any such stop or stand has been officially designated and appropriately signed, except that the driver of a passenger vehicle may temporarily stop therein for the purpose of and while actually engaged in loading or unloading passengers when such stopping does not interfere with any bus or taxicab waiting to enter or about to enter such zone.