CHAPTER 4

UAVs for Bridge Inspection and Monitoring

4.1 Description of UAVs for Bridge Inspection and Monitoring

Around one in three bridges in the United States require repair or replacement, with over 46,000 considered structurally deficient (ARTBA 2022). Maintaining bridges includes detecting damage in order to program repair. Current methods include the following:

• Visual inspection, which requires workers to manually inspect bridges.
• Acoustical techniques using a chain drag or hammer to recognize changes in sound pitch.
• Infrared or thermal imaging, which detects changes in infrared radiation.
• Coring and chipping, which uses drilled cores to assess corrosion.
• Ground penetrating radar, which uses electromagnetic radiation to visualize the subsurface.
• Half-cell potential test, which uses the change in voltage to detect corrosion.

Traditional bridge inspection often involves establishing work zones, rerouting traffic, and using heavy equipment (McGuire 2020).

UAVs have been tested for use in bridge inspection. Initial applications were primarily research efforts (Gillins et al. 2016). For instance, Otero et al. (2015) tested UAVs to monitor bridges and high mast luminaires under different flight scenarios, light conditions, altitudes, and wind conditions. Zink and Lovelace (2015) evaluated infrared photos collected from UAVs to detect bridge defects. Several researchers developed algorithms, such as deep learning for crack detection (Yin et al. 2015, Lei et al. 2018, Wu et al. 2018). Carnegie Melon University and Northeastern University developed a drone that captures camera images and conducts laser scans to create high-resolution bridge models (Gustafson and Sankaran 2019). Researchers at Rutgers University piloted the use of a UAV for the collection of bridge features, with the UAV able to inspect the bridge both from the air as well as underwater (Vuocolo 2017). Figure 4-1 shows an example of bridge inspection using UAVs.

4.2 Examples of UAV Applications for Bridge Inspection and Monitoring

Information about how agencies have utilized UAVs for bridge inspection/monitoring was gathered from three sources: (1) a review of the literature, (2) a survey of agencies, and/or (3) questionnaires/interviews targeted to specific agencies.

Examples of applications involving the use of UAVs for bridge inspection/monitoring were found in the literature review for 12 agencies. The corresponding information is summarized for each agency in the sections below.

The survey discussed in Chapter 3 included questions about bridge inspection/monitoring. Several agencies indicated in the survey that they were using or were piloting the use of UAVs for bridge inspection/monitoring and were willing to be contacted.

From both the literature review and the survey, a total of 24 agencies were identified as having used or piloted the use of UAVs for bridge inspection/monitoring. A list of questions was developed, and the contact person from each agency was emailed a description of the project, a request for a short virtual meeting, and the list of questions. In multiple cases, more than one person at an agency was identified, and each was contacted. The identified contacts were asked to forward the email or notify the research team if someone else at the agency would be better able to provide the information. If no response was received, several follow-up emails were sent. In some cases, the agency provided a written response, and in others the information was gathered through a discussion with the agency contact. Responses were gathered from seven agencies and are presented in the following sections.

4.2.1 Responses from the Survey

A survey was conducted to gather information about the automated processes that IOOs have implemented or are planning to implement, as described in Chapter 3. Agencies were asked about their use of UAVs for infrastructure inspection activities. The most common use of UAVs for inspection activities was bridge inspection, with 58% (n = 19) of agencies having used and 27% (n = 9) having piloted the technology, and with another 3% (n = 1) likely to evaluate the use of the technology in the next 3 to 5 years. Agencies were also asked about the processes that they thought would benefit the most from automation. This could include the use of UAVs, but the question was not specifically about UAV applications. Around 90% (n = 28) of agencies indicated that bridge inspection would benefit from automation.

4.2.2 Florida

One study found in the literature described the use of UAVs for bridge inspection in Florida.

Summary of Literature for Florida

Researchers from the Florida Institute of Technology explored the effectiveness of small UAVs to inspect high mast poles and bridges. This experiment demonstrated UAV use in windy and low-light conditions. The authors found that small UAVs can be controlled from a safe distance and can even detect cracks as fine as 0.02 in. The noted advantages for the use of UAVs for this application were improved safety for workers and motorists and a reduction in cost (Otero et al. 2015).

4.2.3 Georgia

One study was found in the literature that described the use of UAVs for bridge inspection in Georgia. Additionally, the team was able to conduct a targeted interview with the Georgia DOT (GDOT).

Summary of Literature for Georgia

GDOT (Irizarry and Johnson 2019) conducted focus groups to identify tasks that could benefit from the use of UAVs and to suggest other applications. Responses for related tasks indicated that using UAVs could benefit the collection of data to develop three-dimensional (3D) models to detect and assess cracks, assess vertical clearance, and develop 3D steel beam models to compare the as-built structure to the original design.

Summary of Conversations with Georgia

A discussion with GDOT [Demario Hall, Unmanned Aircraft System (UAS) Program Manager, Georgia Department of Transportation, personal communication, August 2023] indicated that it is conducting a pilot study to test the efficacy of UAVs to assess bridge condition. Currently (as of August 2023), GDOT has 30 UAVs with 3D scanning technology. Data from bridges and other infrastructure are collected via UAV, and then 3D models are created using specialized software. GDOT is also looking into several other software packages to process the data. The 3D models can be used to detect whether cracks are present and can also be used in emergency response applications. For instance, an archived 3D model of a bridge can be compared to one created after flooding to make an initial estimate of damage.

The respondent did not have specific estimates of cost but noted that the largest costs are associated with training and software. Costs to purchase UAVs were not considered significant, and maintenance of the UAVs had been relatively simple. Training was noted as the biggest cost because the use of UAVs requires a pilot’s license. Additionally, inspectors need to be trained in how and what to collect. The respondent noted that estimates of the total costs for the use of UAVs need to account for not only the UAVs but also communications equipment, software to turn the images into information, and training.

The pilot project being conducted by GDOT is to evaluate the efficacy of UAVs for bridge inspection and to provide some initial evaluations of accuracy. The next step is to assess the 3D models to further determine accuracy. Moving from the pilot stage to deployment depends on whether a business case can be made, which entails tracking performance indicators such as time and costs. GDOT belongs to a user group with other DOTs in the southeast that shares technologies and lessons learned.

4.2.4 Idaho

No information was available in the literature about the use of UAVs for bridge inspection in Idaho. The team, however, was able to conduct a targeted interview with the Idaho Transportation Department (ITD).

Summary of Conversations with Idaho

A conversation with ITD (Mike Johnson, Idaho Transportation Department, personal communication, August 2023) indicated that it is in the deployment stage for the use of UAVs for bridge inspection. ITD is not deploying UAVs itself; instead, it is currently contracting with three consultants. UAVs are not used to conduct regular inspections but rather to supplement inspections, and their use is limited to specialized situations such as in locations where a human inspector cannot gain access for routine inspection. As an example, UAVs have been used to inspect the interior of a closed box column on a steel truss bridge and the interior of a concrete box on a segmental bridge.

The main barriers to the use of UAVs for bridge inspection include the following:

• Lack of the credibility and value of an arm’s reach inspection,
• Inability to access all locations, and
• Vulnerability to lightning and other factors.

In general, ITD had no plans to use UAVs in lieu of actual inspections. It was noted that they are a tool but recommended that they only be used to supplement arm’s reach inspections when appropriate.

ITD had no immediate plans for increased deployments. However, as technology improves, it will likely increase its use of UAVs.

The consultant testing the UAVs conducts regular bridge inspections, but costs have not been broken down for UAV use separately. As a result, no cost estimates were available from ITD.

4.2.5 Kentucky

One study was found in the literature that described the use of UAVs for bridge inspection in Kentucky.

Summary of Literature for Kentucky

The Kentucky Transportation Cabinet used UAVs to assist in the inspection of the Brent Spence Bridge. The bridge was inspected due to fire damage, and the use of UAVs aided in carrying out the initial inspection (Northern Kentucky Tribune 2020).

4.2.6 Louisiana

One study was found in the literature that described the use of UAVs for bridge inspection in Louisiana.

Summary of Literature for Louisiana

A group of researchers from Louisiana State University carried out a study using a UAV for routine bridge inspection. The researchers suggested that UAVs could facilitate the bridge inspection process by reaching areas that are not possible to access through manual inspection. However, it was found that the UAV system is not a replacement for human bridge inspectors because it can have some issues with the global positioning system (GPS) under the bridge deck and because subsurface cracks in concrete or hollow timber cannot be identified by UAVs (Darby and Gopu 2018).

4.2.7 Maine

One study in the literature described the use of UAVs for bridge inspection in Maine.

Summary of Literature for Maine

The Maine DOT used UAV technology to inspect the Ticonic Bridge. The use of UAV technology minimized the safety hazards for inspectors and decreased traffic impacts. The UAV also provided high-quality images to identify spalling or loose concrete. The Maine DOT and the inspection team decided to inspect the bridge using both a UAV and an under-bridge inspection truck in the future (FHWA 2021).

4.2.8 Michigan

One study was found in the literature that described the use of UAVs for bridge inspection in Michigan.

Summary of Literature for Michigan

The Michigan DOT (MDOT) used UAVs to conduct a manual inspection of a bridge on a four-lane divided highway. MDOT estimated that the traditional inspection method, which takes up to 8 hours to complete and requires a two-person ground crew using heavy equipment, would have cost $4,600. MDOT estimated that one UAV pilot and one spotter was able to conduct the same function in 1 hour for a cost of about $1,200. Additionally, the use of UAVs did not necessitate the closure of lanes, which MDOT estimated would have cost an additional $14,600 (Government Fleet 2019).

4.2.9 Minnesota

One study in the literature described the use of UAVs for bridge inspection in Minnesota.

Summary of Literature for Minnesota

The Minnesota DOT (MnDOT) carried out a project in which four bridges of varying sizes were inspected by UAVs in order to assess the effectiveness of this technology. The study found that this UAV-based technology is more effective for larger bridges, but it also can be of use for short-span bridges and culverts. The study also found that UAVs can be efficient in taking infrared pictures of bridge decks and other elements and that the use of UAVs is a cost-effective option for routine maintenance (Zink and Lovelace 2015).

4.2.10 Nevada

One study in the literature described the use of UAVs for bridge inspection in Nevada.

Summary of Literature for Nevada

Stantec has introduced an innovative bridge inspection method for the Nevada DOT (NDOT) that involves creating 3D models of bridge elements using UAVs. The company also carried out a bridge inspection for the Mike O’Callaghan-Pat Tillman Memorial Bridge (Hoover Dam Bypass) in Nevada (Stantec 2023).

4.2.11 North Carolina

One study in the literature described the use of UAVs for bridge inspection in North Carolina. Additionally, the team conducted a targeted interview with the North Carolina DOT (NCDOT).

Summary of Literature for North Carolina

NCDOT conducted its first bridge inspection using UAVs in February 2021. Operators monitored live high-definition video feeds from drones to evaluate the 10 largest columns on the Marc Basnight Bridge. UAVs were not expected to replace traditional visual inspection; they were instead used to inspect areas of the bridge that are difficult to access during visual inspections. NCDOT used a UAV with detect-and-avoid technology, which allowed the UAV to operate within 1 ft of the bridge structure. This allowed the UAV to fly around pillars, between girders, and inside columns (NCDOT 2021), as shown in Figure 4-1.

Summary of Conversations with North Carolina

A conversation with NCDOT (David Snoke, Inspections and Inventory, Structures Management Unit, North Carolina Department of Transportation, personal communication, August 2023) indicated that it is in the actual deployment stage in terms of using UAVs for bridge inspection. This deployment includes two in-house inspectors who are licensed as drone pilots. UAVs are used to capture photos of the general structure and access hard-to-reach places on good-condition bridges. The information is used to determine whether special access equipment is needed to do a hands-on inspection of those components.

NCDOT noted that the main advantage of using UAVs is the ability to minimize the use of expensive traffic control equipment, which also reduces interference with traffic.

The cost for NCDOT’s use of UAVs for bridge inspection was not easily estimated because NCDOT has a fleet of UAVs that is used for multiple purposes. The use of UAVs is not itemized specifically for the times they are used for bridge inspection.

NCDOT did not have fixed plans for expansion but hoped that more in-house inspectors are able to obtain their pilot’s licenses. It also noted that the need for a license is the main barrier to the use of UAVs because obtaining a pilot’s license requires more technical training than what is needed for bridge inspection. NCDOT also noted a need for guidance from the FHWA on the acceptable use of UAVs for element-level bridge inspection.

NCDOT’s main recommendation for other agencies that may be interested is to proceed cautiously due to the rapidly evolving nature of UAV technology.

4.2.12 North Dakota

No information was available in the literature that described the use of UAVs for bridge inspection in North Dakota. The team, however, was able to conduct a targeted interview with the North Dakota DOT (NDDOT).

Summary of Conversations with North Dakota

NDDOT (Matthew Kurle, North Dakota Department of Transportation, personal communication, August 2023) has been in the testing stage for the use of UAVs for bridge inspection since 2019. The application entails the DOT working with consultants. UAVs are flown to take images that are then used to create 3D models of the bridge being inspected. The objective is to identify defects during bridge inspections. A recent application was a survey of a large bridge over the Yellowstone River which had been struck by a vehicle that damaged an outside beam. UAVs were flown, and a 3D model was created of the damage.

The next step to move into implementation is to create a proof of concept in order to establish funding. NDDOT currently has one UAV in place but plans to have three. It expects to move into implementation within 1 to 2 years. The main barrier is budgeting and flux in the UAV program.

Implementation will likely entail using UAVs for a prioritized list of bridges. UAVs will not be used on all bridges due to factors such as bridge location and design and the ease with which UAV equipment can be set up and broken down at the bridge location. NDDOT also felt that some situations call for more traditional inspection methods. It plans to utilize UAVs in situations where there will be time and cost savings.

NDDOT noted that costs were difficult to quantify because the costs for various models of UAVs fluctuate. However, based on their current application, NDDOT anticipates an annual cost of $10,000 per drone plus the cost of software.

The main advantages to UAVs noted by NDDOT were time-saving, improved safety for inspectors, and the ability to avoid or minimize the use of traffic control. NDDOT noted that it has a mile-long bridge that crews need about 5 days to inspect. NDDOT estimates that the inspection could be conducted in 1 to 2 days with UAVs.

The main challenges to UAV implementation noted by NDDOT were the additional work needed to conduct a bridge inspection in terms of setting up, learning, and using software and creating 3D images. NDDOT also noted that procurement was a barrier when federal funds were used due to requirements to buy American-made UAVs, security, and issues with noncompliant manufacturers. Another challenge was loss of a drone in a river while conducting an autonomous scan. NDDOT also noted that a lack of collision detection software on UAVs is a safety concern and could result in damage to the bridge. Weather also poses a challenge for UAV use.

NDDOT is also looking into artificial intelligence applications to determine the benefits.

4.2.13 Oklahoma

No information was available in the literature that described the use of UAVs for bridge inspection in Oklahoma. The team, however, was able to conduct a targeted interview with the Oklahoma DOT.

Summary of Conversations with Oklahoma

The Oklahoma DOT (Justin Hernandez, State Bridge Engineer, Oklahoma Department of Transportation, personal communication, August 2023) has a single in-house UAV that it has utilized to access bridges on a pilot basis. The UAV is managed by the department’s Internal Media and Public Affairs Division. It has also worked with consultant engineering firms, which have multiple UAVs. The use of UAVs has been limited to supplementing traditional, proven techniques. The Oklahoma DOT noted varying degrees of success.

The main advantage to using UAVs noted by the Oklahoma DOT is that UAVs are effective at wide-angle photography (macroscale) of bridge profiles and decks. However, with the currently available UAV technology, the Oklahoma DOT did not see many advantages over traditional methods for access and inspection. While the Oklahoma DOT currently sees only limited applications, it recognizes that there is potential and believes that UAVs will be most beneficial in focused review and evaluation rather than for exploratory inspection. At this time, the Oklahoma DOT is not planning to move into full implementation. The main barriers are that procurement and operation costs, technological limitations, and the need for training and operator experience outweigh the benefits. The Oklahoma DOT noted that a more realistic expectation of what UAVs are capable of is needed because the promises of equipment/software providers may outpace actual capabilities. It felt that the technology is emerging and holds real potential for in-depth assessment but felt that the probability of full deployment for the purposes of routine bridge inspection is not realistic in the near term.

The UAV utilized to conduct bridge inspection is maintained and operated by another division within the Oklahoma DOT. As a result, detailed costs were not available. Work with consultants was not a task for the Oklahoma DOT, so it was not able to capture that cost either.

4.2.14 Oregon

One study was found in the literature that described the use of UAVs for bridge inspection in Oregon.

Summary of Literature for Oregon

Researchers in Oregon evaluated the use of UAVs for bridge inspection to document the capabilities and effectiveness of UAVs (Gillins et al. 2018). Three different UAV models were tested and evaluated on five bridges between 2015 and 2017. The researchers determined which bridges were suitable for UAV inspection. Their main findings include the following:

• In-field inspection time was reduced by an estimated 20% for those bridges suitable for UAV inspection, however an estimated 30% increase in in-office time to conduct flight planning, and data downloading, processing, and analysis was noted. As a result, Oregon estimated an overall reduction in personnel time of 10%.
• An estimated average savings of $3,900 for personnel time, $2,800 for equipment rental, and $3,500 for traffic control was found, resulting in a decrease of $10,200 for bridges suitable for UAV inspection.
• Using a simplified approach, a benefit-cost ratio of 9:3 was estimated for bridges suitable for UAV inspection.

4.2.15 Pennsylvania

No information was available in the literature that described the use of UAVs for bridge inspection in Pennsylvania. The team, however, was able to conduct a targeted interview with the Pennsylvania DOT (PennDOT).

Summary of Conversations with Pennsylvania

PennDOT is in the testing stage for the use of UAVs for bridge inspection. PennDOT has tested six different types of UAVs, including smaller/compact and larger commercial varieties. Primarily, PennDOT was evaluating ease of use, maneuverability, cost, camera function, and defect detection. After the pilot program, PennDOT is planning to move into bridge inspection with its small fleet of UAVs.

PennDOT cited the main advantages as safety and decreased impact on the public. The estimated cost for UAV use from the pilot study was approximately $2,000 per UAV.

One of PennDOT’s recommendations for assessing the use of UAVs was to test different types of UAVs at different locations. PennDOT also suggested identifying the bridge defects of interest first and understanding the planning aspects of using UAVs for bridge inspection. This includes understanding what permissions are needed.

PennDOT noted that training for operators is critical. In addition to knowing how to fly, pilots also need to understand and be prepared for the challenges of flying around structures. Inspecting bridges is a complex process, which entails proximity to obstacles, varying wind conditions, and increased risk. As a result, proper preparation for pilots is needed before embarking on missions.

4.2.16 South Dakota

One study in the literature described the use of UAVs for bridge inspection in South Dakota.

Summary of Literature for South Dakota

A group of researchers investigated the effectiveness of UAVs by conducting a study to inspect a timber arch bridge in South Dakota. High-quality images and videos were collected, and a pixel-based damage measurement process was used to assess the damage. The visual inspections from the UAVs were compared with past manual inspection reports to validate the effectiveness of UAVs for bridge inspection (Duque et al. 2018).

4.2.17 Vermont

No information was available in the literature that described the use of UAVs for bridge inspection in Vermont. The team, however, was able to conduct a targeted interview with the Vermont Agency of Transportation (VTrans).

Summary of Conversations with Vermont

VTrans is in the testing stage for the use of UAVs for bridge inspection and has tested three UAVs. It plans to move to implementation within 2 years. One of the main findings from the pilot program was that bridge inspectors should be trained to be UAV pilots rather than training UAV pilots to inspect bridges. VTrans also reported that not all bridges are good candidates for inspections by UAV and that, due to equipment limitations, some types of drones were good for some types of bridges and others were better for other types of bridges. This suggests that a one-size-fits-all approach to using UAVs is not effective.

The main advantage cited by VTrans regarding the use of UAVs was that UAVs avoid the need to use a Servalift or ladders to inspect bridges. Staging is also more effective. The use of UAVs results in improved safety for personnel.

VTrans estimated a cost of approximately $10,000 per year for one drone, which included the software to operate it and training for one operator.

One suggestion from VTrans was to encourage bridge inspection teams to become trained to pilot UAVs. VTrans also suggested leveraging research that has already been conducted [e.g., NCHRP, New England Transportation Consortium (NETC)] to formulate best practices. Additionally, VTrans suggested that an agencywide vision is needed to support the use of UAVs in all areas of transportation. Buy-in at the top is needed so that personnel are willing to prioritize efforts to move this technology forward.

4.2.18 Wisconsin

One study in the literature described the use of UAVs for bridge inspection in Wisconsin.

Summary of Literature for Wisconsin

The Wisconsin DOT (WisDOT) carried out a pilot project to evaluate the effectiveness of UAVs for bridge inspection. The project showed that using UAVs led to safety benefits for bridge inspectors and remote pilots. The traffic impacts of bridge inspections were also reduced because no road closures were needed. Data collected from the UAVs were useful in identifying narrow cracks and minor defects. Overall, the project illustrated the effectiveness of UAV use in terms of enhanced safety and the collection of high-quality images (Michael Baker International 2017).

4.3 Summary of Applications for UAVs for Bridge Inspection and Monitoring

Fifteen states were found to have piloted or deployed UAVs for bridge inspection/maintenance, with the majority conducting deployments. Common applications included the use of UAVs to collect images, collect data to create 3D models, and inspect areas that are hard to reach.

4.3.1 Advantages and Suggestions

Several advantages were noted in both the literature and conversations with agencies, with the main advantages to the use of UAVs for bridge inspection/maintenance including the following:

• Minimized use of expensive traffic control and minimized interference with traffic;
• Decreased inspection times;
• Ability to capture data in near real time;
• Fewer personnel and less equipment required for inspections;
• Location of workers off the roadway, which improves safety for both inspectors and the traveling public; and
• Ability to access locations that are difficult for human inspectors to reach.

Suggestions from agencies include the following:

• Encourage bridge inspection teams to become trained to pilot UAVs.
• Leverage research that has already been conducted (e.g., NCHRP, NETC) to formulate best practices.
• Develop an agencywide vision to support the use of UAVs in all areas of transportation.
• Secure leadership buy-in so that personnel are willing to prioritize effort.

4.3.2 Disadvantages

The main disadvantages to the use of UAVs for bridge inspection/maintenance include the following:

• Lack of the credibility and value of an arm’s reach inspection,
• Inability to access all locations,
• Vulnerability to lightning and other factors,
• Limited function in locations where GPS is blocked, and
• Training required for the use of both UAVs and software.

4.3.3 Challenges

Targeted discussions with agencies found several challenges to implementing UAVs for bridge inspection. One agency noted that the requirement to buy American-made drones made purchasing UAVs difficult. Another challenge noted was the training of UAV pilots. Several agencies noted that getting pilots certified is reasonably easy and that piloting drones is straightforward. However, training pilots on what needs to be collected and how to fly in close proximity to structures and in varying wind conditions was challenging. Similarly, one agency indicated that bridge inspectors should be trained to be UAV pilots rather than training UAV pilots to inspect bridges because pilots must understand what they are looking for.

The use of UAVs in the vicinity of traffic could pose a risk if UAVs enter vehicles’ right of way. Additionally, the presence of UAVs can be distracting to drivers.

Challenges were also noted in terms of budgeting and the flux in UAV programs. One agency felt that the costs of UAV technology, its technological limitations, and the need for training and operator experience outweighed the benefits.

4.3.4 Costs

Most of the sources did not have specific cost estimates. In many cases, UAVs are owned by an agency and utilized for multiple purposes, which makes it difficult to isolate the costs for a given purpose. One source did mention purchase costs of around $10,000, which did not include software, and another agency estimated $2,000 per UAV. Another agency also mentioned a cost of $10,000 per year for one drone, which included the software to operate it and training for one operator. One of the agencies interviewed reported that the cost of UAVs was reasonably low and that maintenance could be accomplished in-house.

However, while the cost and maintenance of UAVs is not prohibitive, the total cost includes costs for pilot training and licensing, training to operate the UAVs, communications equipment to download data from the UAVs, and software to turn the data into useful information. Several agencies noted that the largest cost was training pilots to operate the UAVs. As a result, it was difficult to estimate total costs.

One source did estimate that the cost to conduct a typical bridge inspection on a four-lane divided roadway was around $4,600, with the cost of closing lanes estimated at an additional $14,600. The estimated cost for the use of a UAV for the same inspection was around $1,200 (Government Fleet 2019). Another source indicated that a typical bridge inspection took 5 days, which could be shortened to 1 to 2 days with the use of UAVs. Another source indicated savings of around $10,000 when UAVs are used for bridge inspection, with a benefit-cost ratio of 9:3. However, it seemed that only costs associated with the actual inspection were included in that estimate.

4.3.5 Status

A number of agencies have piloted the use of UAVs for bridge inspection in the United States, while several noted that they had implemented their use. Several indicated that they were not fully ready to replace traditional bridge inspection. Many planned to use UAVs to supplement rather than replace bridge inspection.