(a) The number of miles traveled that are eligible for reimbursement under this subchapter may not exceed the number of miles of the most cost-effective reasonably safe route between the origin of the state employee’s travel and the final duty point of the state employee. If a state employee conducts official state business at duty points between the origin of the state employee’s travel and the final duty point, the most cost-effective reasonably safe route between the origin and the final duty point shall include the intermediate duty points.