The use of small Unmanned Aircraft Systems (UAS) within transportation agencies for applications such as bridge inspections has seen growth due to potential time and cost savings as well as safety benefits. Researchers in Oregon evaluated and documented the effectiveness of inspecting bridges with UAS. The primary goal was to document the capabilities and limitations of performing structural inspections with UAS. Following a literature review and a detailed analysis of UAS components, three different UAS models were tested and evaluated on five bridges and three communication towers from 2015 to 2017. The results were used to compile recommended safety and operational procedures. The findings were used in conjunction with Oregon DOT data to perform a cost-benefit analysis for the use of UAS in bridge inspection.
A cost-benefit analysis was conducted for performing inspections for communication towers and bridges with the use of UAS. Baseline costs for bridge inspections conducted without the use of UAS were established by compiling existing data from Oregon DOT. Findings from the study and consultations with Oregon DOT personnel were used to establish which project costs could be reduced through use of UAS, and to estimate percentage reductions in those categories. Finally, the percentage of bridges suitable for UAS inspection were determined. In the analysis, the costs of three UAS was considered in addition to other supporting costs including maintenance and disk space for storing the large volumes of imagery collected in a UAS-assisted inspection.
- The in-field inspection time was estimated to be reduced by 20 percent for bridges suitable for UAS inspection. However, an associated increase in office time of 30 percent was estimated due to flight planning and data downloading, processing and analysis tasks. Based on the average office and field times from the Oregon DOT baseline cost data, applying these percentage changes yielded an overall reduction in personnel time of 10 percent.
- By implementing inspections using UAS, there is an estimated average savings of approximately $3,900 for personnel time, $2,800 for equipment rental, and $3,500 for traffic control. For bridges suitable for UAS usage, these results represent a decrease in bridge inspection costs of $10,200 per project.
- The study team used a simplified approach, without discounting, for estimating a Benefit-Cost ratio for the use of UAS for bridge inspections, considering the overall level of uncertainty. The benefits for Oregon DOT over one year were estimated at $1,191,360 compared to estimated costs of $127,437, resulting in a Benefit-Cost ratio of 9.3.