The intent of the Legislature is for the structuring of maturity schedules and escrow accounts which will allow the greatest amount of revenues to be used for current construction of highways, while retaining a sound program of retiring the refunding bonds in an economically feasible manner. It is the further intent that all funds available under any of the provisions of Chapter 478, Laws of 1978, shall be invested at all times when not needed to pay the expenses authorized under the provisions of Chapter 478, Laws of 1978, and to pay the principal of and the interest on any bonds payable under the provisions of Chapter 478, Laws of 1978, as they become due.