The board of supervisors of counties having a population of not more than twenty-two thousand (22,000) nor less than fifteen thousand (15,000) as shown by the 1970 federal census and having an assessed valuation in excess of Twenty Million Dollars ($20,000,000.00) in 1970 and being traversed by Interstate Highway No. 55, may, in the discretion of the board, set aside, appropriate and expend moneys from the general fund to be used solely for defraying the cost of providing public ambulance service as authorized by Sections 41-55-1 through 41-55-11.