The county treasurer shall pay from the general fund of the county the traveling and other incidental expenses of county highway commission members that are actually and necessarily incurred and all other expenses incurred either by the board of supervisors or by the county highway commission under this article until there are sufficient monies in the highway improvement fund derived from the sale of bonds with which to pay the expenses. The county treasurer shall reimburse the general fund of the county from the highway improvement fund. After there are sufficient monies to pay for the expenses, all expenses shall be paid from the highway improvement fund.