In the event no final rate determination has been made upon the schedule for new rates within ten (10) months after the date the schedule for new rates was filed with the Arkansas Department of Transportation, the public utility may put the suspended rate into effect for all bills rendered thereafter immediately upon the filing of a bond to be approved by the department payable to the State of Arkansas in such amount and with sufficient security to insure prompt payment of any refunds to the persons entitled thereto, including an interest rate as determined by the department not to exceed the maximum interest otherwise allowed by law, if the rate or rates so put into effect are finally determined to be excessive. There may be substituted for the bond other arrangements satisfactory to the department for the protection of the parties interested.