Cost-Effective Bridge Safety Inspections Using Unmanned Aircraft Systems (UAS)

Throughout the world, many highway workers and road users face safety hazards associated with bridges. ASCE estimates that one in nine of the nation’s bridges are rated as structurally deficient, with an average age of 42 years. In an effort to reduce the risks associated with bridges, the Federal Highway Administration (FHWA) requires states to perform a detailed, visual inspection and inventory of all federal-aided highway system bridges once every two years. At times, mandatory inspections are costly and dangerous, as inspectors need to stand in platform trucks, bucket trucks, or under-bridge inspection vehicles in order to access and view necessary bridge elements. Furthermore, some inspections require extensive climbing, temporary scaffolding and ladders, or rescue boats. Unmanned aircraft system (UAS) technology provides a cost-effective and safe method for remotely performing visual inspections and inventorying of bridges. UASs are capable of flying a pre-programmed flight path, and can carry high resolution digital cameras and/or other sensors. During flights, operators can view live video from the camera on a monitor or through live video goggles. In addition, digital imagery collected during flights can be mosaicked, georeferenced, and converted into 3D point clouds for detailed spatial inventorying. This paper presents the methodology and results of inspections of a bridge in Oregon using a multicopter UAS. Because multicopters can be flown close to objects, are easy to maneuver, and can hover in place, high-resolution remote sensing data can be collected from multiple advantageous viewing angles. Such data is similar to what can be seen visually by an inspector at arm’s length from the bridge. Recommendations for safe and effective flights are given, and the capabilities and limitations of UAS bridge inspections are discussed. It will be shown that today’s UAS technology has great potential for performing remote and safe, visual inspections of structures.