What is the difference between 'Inventory Rating' and 'Operating Rating' in bridge load rating?

The difference between 'Inventory Rating' and 'Operating Rating' in bridge load rating lies in the level of safety margin and the purpose for which each rating is used. Inventory Rating represents the load level that can safely utilize the bridge for its design life, reflecting the capacity based on original design assumptions and material properties with minimal damage or deterioration. It is a conservative estimate intended to ensure the long-term durability of the structure. Operating Rating, on the other hand, represents the maximum permissible load level that the bridge can carry, allowing for some level of acceptable risk and minor permanent damage. This rating is higher than the Inventory Rating and is used for evaluating the ability of the bridge to carry occasional overloads or permit vehicles. Essentially, Inventory Rating is for routine traffic and long-term structural health, while Operating Rating is for infrequent, higher loads with a slightly reduced safety margin.