It shall be unlawful to operate any vehicle which is so loaded or in such a condition that the operator does not have a clear vision of all parts of the roadway essential to the safe operation of the vehicle. Any vehicle which is constructed or loaded so that the driver's view of the roadway to the rear is obstructed shall be equipped with a mirror so attached as to give him a view of the roadway behind.
('68 Code, § 65.29) Penalty, see § 70.99