The board shall levy annually a tax upon the taxable property of such county to be used for road and bridge purposes; and the tax collector shall collect such taxes at the time and in the manner state, county, and other taxes are collected. All laws for the enforcement of the collection of other taxes shall apply to the collection of such taxes, and the tax collector's bond shall cover the same in like manner. When such taxes are collected, they shall be paid into the county depository as other taxes, and in like manner shall be covered by the bond of the county depository. Such funds shall be kept as a separate road fund and shall be paid out only on allowances and warrants of the board of supervisors for said purposes.