Any county in this State having a population of 500,000 or more inhabitants, by one or more resolutions of its county board adopted from time to time, may incur indebtedness and issue bonds for the purpose of constructing superhighways, which bonds are hereinafter referred to as superhighway bonds, in an amount or amounts not exceeding in the aggregate seventy million dollars without submitting the question to the voters of such county for approval. The superhighway bonds may be made registerable as to principal and may bear interest at a rate not to exceed four per centum annually, payable at such time and place as may be provided in the bond resolution or resolutions. The superhighway bonds shall remain valid even though one or more of the officers executing the bond ceases to hold his or their offices before the bonds are delivered.
     The bonds shall be sold to the highest and best bidder for not less than their par value, upon sealed bids. The County Board shall, from time to time, as bonds are to be sold, advertise in a daily newspaper of general circulation in such county for proposals to purchase the bonds. Each of such advertisements for proposals shall be published at least 10 days prior to the date of the opening of the bids. The County Board may reserve the right to reject any and all bids.