Nondestructive testing (NDT) of transportation infrastructure is critical for evaluating existing material deficiencies and suitability for safe continued service. While NDT inspection programs dramatically increase the safety and integrity of our infrastructure, access requirements in performing these inspections introduces risk. Inspection sites often require access to elevated areas via equipment such as personal fall protection (safety harness and lanyard), ladders, scaffolding, inspection trucks with elevated baskets, rope work, catwalks, and rigging. Working at height creates a safety risk to the worker performing the inspection, and cause work zones and traffic detouring creating vulnerable environments that increase the potential for crashes. Unmanned aerial vehicles (UAVs), or drones, can improve the safety and efficiency of transportation infrastructure by performing the inspection with workers safe on the ground. In 2016, the American Association of State Highway and Transportation Officials (AASHTO) reported that 17 state Departments of Transportation (DOT) had either used or tested drones (i.e. UAVs) for work within the transportation industry. The Michigan DOT and Michigan Tech Research Institute conducted a study in 2014 which reported that drones were a safe, reliable, and cost effective tool for visual bridge inspections. Drone inspections thus far have been limited to visual testing (VT). While VT is a primary method of inspection, it is not sufficient in identifying or further evaluating material deficiencies such as metal thickness, small fatigue cracks in welds, or subsurface flaws. To adequately detect these deficiencies, advanced inspection NDT methods, such as ultrasonic testing (UT), are required. Aerial robotic systems have been developed to perform advanced NDT inspection of materials at height. Emergence of this technology is discussed in reference to the transportation industry.

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