Through years of hard use and shrinking maintenance funding, the United States' bridge infrastructure system has been rapidly deteriorating. A significant percentage of the nation's approximately 600,000 bridges are categorized as structurally deficient or functionally obsolete. In fact, the National Bridge Inventory (NBI) database reveals that approximately 87,000 bridges possess structurally deficient characteristics. The large number of structures deemed structurally deficient will require extensive repair and possible reconstruction. The cost of rehabilitating or replacing these structures will stretch limited resources, but is necessary to ensure safety and reliability. Current bridge inspection standards require bridges to be inspected at least once every two years. The inspector can shorten the inspection frequency if the two-year inspection period is deemed inadequate due to visible signs of distress in the structure. Inspections are done mainly through a visual inspection where the inspectors use their judgment, knowledge and experience to categorize the condition of the bridge. Visual inspection practices can be extremely subjective and lead to inconsistent results depending on the inspector. The subjectivity of the inspection process makes it difficult to collect consistent bridge condition data. By introducing remote sensing techniques such as light detection and ranging (LiDAR) into the current inspection practice, the variability in inspection results could be reduced, allowing a more accurate determination of bridge condition and better allocation of funding.
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