A bridge must be posted for a restricted load limit when a load rating analysis and/or posting evaluation, as required by the AASHTO Manual and this code, indicates that a bridge does not have sufficient live load capacity to safely carry full legal traffic loads. A safe load level for a bridge is calculated by ascertaining the limits defined by the inventory and operating load rating levels and using the operating load rating as the upper limit. However, in no case shall loads be allowed on a bridge which exceed the bridge's operating rating capacity.