The taxes levied by a highway board shall be extended on the general roll by the county assessor in a separate column at the rate fixed by the highway board and certified by the secretary of the highway board, at the same time the county taxes are extended. The taxes shall be carried into a column of aggregates and shall be collected by the tax collector of the county at the time and in the manner provided by law for collecting county taxes. The tax collector shall have the same powers conferred upon him respecting the collection of highway district taxes and the sale of delinquent property as are conferred respecting the collection of other county taxes.