An approach to estimate the indirect economic loss due to damaged bridges within the highway system from an earthquake event is presented. The indirect cost considered refers to the increased highway transportation cost only. The study zone covers the St. Louis metropolitan area and its surrounding suburban regions. An earthquake scenario centered in St. Louis, with a magnitude 7.0 is used. The direct earthquake loss was primarily damage to bridges, which causes an increase in travel time and distance within the transportation network. This information is then used as input for the indirect loss model. The indirect loss is examined from an economic perspective. The results reveal that the indirect loss is significant when compared to the direct loss resulting from bridge damage. From the study results, a transportation network planner can prepare an appropriate preventive action plan (such as choosing alternative routes for potential damaged links, as well as reinforcing possible high damage bridges) to reduce the potential losses before the earthquake occurs.