Estimating the marginal costs of bridge damage due to overweight vehicles using a modified equivalent-vehicle methodology and in-service data on life-cycle costs and usage

Civil infrastructure managers have a profound interest in knowing the costs of infrastructure degradation caused by user operations that exceed statutory limits; that way, they are better informed to establish or revise policies related to permit fee structures for such extra-legal operations. In the specific context of vehicle weight permitting for highway bridges, past determinations have typically relied largely on bridge damage simulation using theoretical relationships between the loading and failure modes. Unlike the theory-based simulations, empirical data analysis uses observed field data and therefore are expected to yield more intuitive insights about the actual relationship between in-service loading patterns and their damage (and the cost of repair thereof). A few past studies have used such empirical approaches with some success but have generally been stymied by practical considerations including the lack of adequate translational relationships between the vehicles operating on the road and the vehicle classes typically considered in load analysis. Also, the overweight (OW) cost differences across different bridges attributes (material type, design type, functional class, and age) remain to be investigated. In a bid to overcome these limitations, this paper uses observed in-service data for vehicle loads and the life-cycle costs associated with bridge deterioration repair. The proposed methodology includes a technique that correlates AASHTO design vehicles to FHWA vehicle classes, estimates the total life-cycle cost of bridge upkeep, and allocates this cost to each user group (vehicle class) based on the axle configuration and usage frequency (vehicle-miles travelled) of that class. For each vehicle class, the marginal cost of bridge damage is determined on the basis of the incremental cost responsibility (as a result of adding that vehicle class to the traffic stream) and the typical traffic volume of that vehicle class, and were found to range from $0.01 to as much as $36.35per ft. length per pass of bridge, depending on OW class, and bridge functional class, material type, and age. The paper quantifies the extent to which bridge damage cost due to an overweight truck is influenced by the attributes of the truck and the bridge. The results can be of help to agencies seeking to formulate, update, or evaluate current or future OW permitting policies from the perspective of highway bridge damage among other impacts. This effort is considered timely in the current era when several highway agencies are considering relaxation of their OW permitting policies as a part of efforts to project a business-friendly image in a bid to spur economic development in their states.