From and after the adoption of the master plan or portion thereof and its proper certification and recording, then and thenceforth no improvement of a type embraced within the recommendations of the master plan shall be constructed or authorized without first submitting the proposed plans thereof to the county planning board and receiving the written approval and recommendations of the board; except that this requirement shall be deemed to be waived if the county planning board fails to make its report and recommendations within forty-five days after the receipt of the proposed plans. If a development or public improvement is proposed to be located in the unincorporated territory of the county by any municipality, county, public board or commission, the disapproval or recommendations of the county planning board may be overruled by the county commission, which shall certify its reasons therefor to the planning board, nor shall anything herein interfere with such development or public improvement as may have been, or may hereafter be, specifically authorized or permitted by a certificate of public convenience and necessity, or order issued by the public service commission, or by permit of the county commission after public hearing in the manner provided by section 64.231.