Private automobiles with adequate insurance coverage may be used for official travel only when it is to the best interest of the authority. Governing factors will be the availability, cost and schedules of transportation by common carrier. Use of private automobiles is generally not justified on a cost basis unless one or more passengers, who would normally have reimbursable transportation expenses, accompany the driver. If the authority determines that the use of a privately owned automobile is to its advantage and properly authorizes its use, reimbursement at a rate equal to that allowed to State employees at that time will be allowed for mileage traveled on official business. However, if the authority determines that the per mile rate is not to its advantage, reimbursement for use of a privately owned automobile can always be made to the extent of the prevailing first class fares per railroad mile charged by common carriers. Charges for garage, parking, gasoline, accessories, repairs, depreciation, antifreeze, towage and other similar expenses will not be allowed. Bridge, tunnel and highway tolls are reimbursable. Receipts for such tolls are required to be attached to the voucher. New York Thruway charges are reimbursable but not in excess, during any one year, of the cost of a yearly permit. Toll charges will be considered in determining whether use of automobile is to best interest of the authority.