It is unlawful for any person to operate or load, or cause to be operated or loaded, any vehicle upon any public highway within the jurisdiction of the city in which the contact points of the material being hauled are less than six inches (6") from the top of the bed, unless the vehicle is sufficiently covered or tied down so as to prevent such materials from littering, spilling, falling, discharging, or otherwise escaping therefrom upon the streets, sidewalks, and gutters of the city. This section shall not apply to official street maintenance, construction, or snow removal crews. (Ord. 96-10 § 1: prior code § 11-358(B))