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Cutting the Cost and Time for Stockpile Surveys in Half with Drones

Cutting the Cost and Time for Stockpile Surveys in Half with Drones

By Sally Huynh

Today, drones are delivering survey-grade accuracy in a fraction of the time at half the cost of conventional inspections. State transportation agencies are discovering that the return on investment in drone technology is attractive regardless of state geography and size, from populous states like Ohio and Minnesota to small, rural states like West Virginia.

Other common department of transportation uses for drones include traffic monitoring, disaster response, construction progress updates, ice control, snow removal, and inspections of pavement, high-mast light poles, and bridges. When West Virginia’s transportation department started to consider using drones for some of their work, they had to overcome some objections. “Just three or four years ago, if you were working with photography drones for mapping, you were finding the data to be what we called geographic information system (GIS) at best,” says Travis Long, chief of surveys at West Virginia Department of Transportation (WVDOT). 

But West Virginia’s Environmental Protection Agency (EPA) was already delivering impressive results with drones and it caught WVDOT’s attention. “Between 2017 and 2019 things greatly improved with the mapping software,” Travis notes. “The accuracy and the ways to verify the data have become easier.” 

Since WVDOT launched a proof-of-concept program in 2018, the early skepticism about drones has given way to enthusiasm. The agency reports it is achieving remarkable gains in accuracy, efficiency, cost savings, and safety for one of its most onerous tasks. Here’s how the department of transportation transformed what has always been expensive, accident-prone work—surveying aggregate stockpiles—for the better with drones. 

Replicating Drone Use Established by the State EPA

In many states, the gateway agency for drones is the department of transportation. In West Virginia, the state EPA was the early adopter, turning to drone operations for watershed delineation and reclamation work estimates. 

To cut the cost of acquiring high-quality GIS data as part of reclamation site surveys, West Virginia EPA (WVEPA) started using survey-grade GPS and advanced photogrammetry software to analyze images captured by drones. The high-resolution data on reclamation sites they produced quickly proved the accuracy and value of the drone program. 

It also created a much more efficient workflow. “We record video showing before and after shots of reclamation sites, and we save a lot of time going back and forth to sites, because decision-makers can review the drone HD video remotely,” says Mike Sheehan with the Office of Special Reclamation.

West Virginia Department of Transportation began using drones to survey 177 aggregate stockpiles, analyzing nearly a dozen classes of materials.

Getting Buy-In for Drones at the DOT

Management at the transportation department was nevertheless wary about the potential risks and liability of using drones. “If someone on a road crew dropped a wrench off a bridge and it busted a windshield on a car below, everybody knows our insurance would pay for that,” explains Travis. “And other than that person’s supervisor and maybe one level higher, no one would hear about it. But if I did the same amount of damage to the same windshield with my drone, the incident’s going to go all the way up the chain to management, and it’s probably going to make the news because it’s a new technology.”

With this kind of attention on the program, Travis and his team put a big emphasis on making sure they had the right pilots. It brought up a question many government agencies face early on: whether to hire new or outside drone pilot talent or train in-house experts on how to fly. 

While both approaches have worked well in other states, the West Virginia leaders wanted to handpick their team. Some had lots of flight hours and some had none. Pilots were paired with experienced surveyors and as the program continues to mature, WVDOT is moving toward cross-training surveyors as pilots.

The WVDOT drone team also emphasized starting small and not reinventing the wheel to gain initial approval. “Get through the part that none of us likes to do—the policy and the standard operating procedures—and get that done quickly. Borrow from what others have done and make sure you tailor it to what fits your program.”

Mitigating Public Misperceptions About Drones

“Here in West Virginia, if people don’t know what something is, they tend to shoot it,” says Travis. “One of the frequently asked questions on the state EPA site was, ‘what happens if I shoot this drone down?’”

To get ahead of public misconceptions of what they were doing with drones, WVDOT also published a FAQ. Despite this and other public information efforts, “In our first six months, we were hit with a Freedom of Information Act request from a property owner who asked for all of our drone footage. We had to give them all of the data, some 25,000 JPEG images.”

Surveying Stockpiles with Increased Accuracy, Speed and Safety

That was one of a few bumps in the road during the agency’s three-month trial stage. Surveying some of WVDOT’s 177 aggregate stockpiles was the department’s first use case. State highway departments store large piles of crushed rock, sand, salt, and gravel for road building, maintenance, and winter traction. Constructing a two-lane asphalt highway requires nearly 25,000 tons of crushed stone per mile.

West Virginia’s stockpiles include roughly a dozen classes of materials. These stockpiles must be physically surveyed annually to get an inventory. Until drones, such volumetric calculations have been completed in a few ways. One involves counting the number of trucks carrying bulk material, a method that one company found can cause inaccuracies of as much as 20 percent. Alternatively, crews relied on surveyors to measure the piles, which required them to climb around hazardous stacks of shifting material.  

“It’s always been a project that none of our surveyors like to do, because walking on gabion piles is a good way to get your ankle broke or break some piece of equipment. And then nobody believes the data because they’ve been counting trucks or tonnage,” explains Travis. The WVDOT survey team recognized potential for drones to speed up this process, reduce risk, and increase accuracy. 

Travis’ team made a small $25,000 investment in equipment and pilots. They set up a data model to verify the data they collected. Crews flew drones around stockpiles and quickly captured extensive imagery. These images were stitched together with software that builds 3D models of the piles. These models can easily calculate the volume of stockpiles nestled against hillsides or inclining slopes, a task that’s difficult to do accurately using traditional methods. The team compared the data collected by drone to ground control points, and checked physical measurements in the model to confirm data accuracy.

“We were so impressed,” says Travis. “Surveys of stone and dirt, stockpiles that have a lot of differential in photos, were far more accurate than we could have gathered from surveying.” The work was also completed more than twice as fast. “We would typically have 21 survey crews working on this project, and it would usually take us more than two weeks to complete it. When we took it on with drones, it only took us nine days to collect this data, process it, and report results. This is the best way to survey stockpiles.”

Calculating ROI for Drone Stockpile Surveys

The strong return on investment the West Virginia team demonstrated early on really gave the program traction. WVDOT calculated it by comparing the cost of conventional surveying of stockpiles with surveys using drone technology. The conventional method took 42 surveyors 15 workdays, at a cost of about $378,000. With drones, the same workload took seven drone pilots only nine workdays, costing nearly $35,000. The department saved more than $343,000 in a single month. 

Expanding to Other Use Cases

Considering aggregate is one of the biggest materials used in construction projects, stockpile inspections are a logical first drone use case for many public agencies. In fact, about 50 percent of all aggregate is used for publicly funded construction projects. That includes highways, water and sewer systems, public buildings, airports, and other county and municipal public works projects.

Today, WVDOT is considering expanding its drone programs to uses they think could provide more efficiencies and greater accuracy for the department:

  • Construction material cost estimates such as quantity takeoffs
  • Surveying and topographical maps as part of designing new road routes
  • Road safety assessments using point clouds
  • Drone-based LiDAR surveys to discover delamination of roadbeds undetectable to the naked eye

From surveying aggregate stockpiles to inspecting bridges, drones are transforming what have often been expensive, accident-prone tasks for state transportation agencies. In spite of initial uncertainty, WVDOT’s experiment of using drones quickly expanded to a department-wide program, demonstrating benefits ranging from increased speed and accuracy to substantial cost savings early on. Drone advancements will continue to unlock new and more powerful use cases and following WVDOT’s steps of generating positive public perception and taking after other transportation agencies’ drone programs will help ensure your team is well positioned for growth and innovation in the future.    

Sally Huynh is the Senior Customer Marketing Manager at Skyward, a Verizon company. Sally is a professional marketing manager with a history of delivering successful programs that support company goals for customer acquisition, cross-selling, and retention. She also specializes in customer-focused marketing activities that build advocacy and loyalty while creating a world-class experience through the entire customer journey. When Sally is not being a fierce advocate for Skyward customers, she enjoys hikes with her best four-legged pal, Kona, and flies her Mavic to capture the beautiful Pacific Northwest.

This article was originally published in May 2021.