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MnDOT to test bridge-inspecting drones in Duluth

A drone flies by a bridge during a July test to see if the unmanned aircraft can be used to help inspect Minnesota bridges. (MnDOT photo)

ST. PAUL — Flying a small drone around a bridge may be safer and less costly than traditional ways of inspection, with Minnesota officials planning more tests to gauge their usefulness.

After a summer drone test, next up will be a fall test that will include inspecting the state's longest bridge, the 7,975-foot John A. Blatnik Bridge in Duluth. If that and other fall tests are successful, Minnesota could become the first state to use the unmanned aircraft to help inspect bridges.

"We are just looking at more innovative technologies to help us," said Jennifer Zink, Minnesota Department of Transportation bridge inspection engineer.

Although no drone bridge inspectors are in use in the country, Zink said the technology could provide benefits: “Using drones could help MnDOT decrease the rising costs of bridge inspection while minimizing risks associated with current bridge inspection methods.”

Four bridges, of a variety of styles, were used in a summer test, in Chisago County, Orono, Little Falls and Stillwater.

It showed MnDOT officials that a drone could be considered when a hands-on inspection is not required and could be used when an area difficult to reach needs to be photographed. Drones can provide still, video and infrared photography.

Zink said advantages of drones include less need to block a lane of traffic while a truck with a long, articulated arm suspends a basket containing human inspectors under a bridge.

The fall test, to be conducted with a drone better equipped for inspection duty than the one used in July, will answer many of the remaining questions, Zink said, including how much money drones could save.

Drones are not being studied as a replacement for human inspectors, Zink said. Safety and costs are the main reasons, she said.

In some cases, she added, human inspectors might operate drones to extend their reach from their perch in a basket under a bridge. However, any time a drone shows a potential problem or its view is blocked, a human inspector would check out the area, she said.

Drones could be used to inspect culverts and other enclosed areas difficult for people, Zink said. The drone being used this fall could sense anything, such as a bird, approaching it and immediately return to its home base. The drone also will have bumpers on its rotors to reduce any damage or injury.

Drones like those MnDOT would use probably would be 18 to 20 inches in diameter.

The Blatnik bridge will be inspected this fall the traditional way, Zink said, but a drone also will be used for comparison purposes. Being the longest Minnesota bridge, and high above the water, the Blatnik inspection could prove a significant test of the technology.

Much of the Blatnik inspection is expected to be routine, she said, where the drone likely would do fine. But since "you can see real time when it is up there," a person could be sent to look at any issues the drone camera relays. Some parts of the bridge, and other bridges, must be closely inspected in person regardless of whether a drone is used.

There are about 20,000 bridges in Minnesota and more than half are inspected each year. Local governments, which own more of those bridges than does the state, might be able to use a state-owned drone if MnDOT buys into the program.

While no states use drones to inspect bridges, the topic has long been discussed. The American Society of Civil Engineers Website reports Tufts University professors are working on a system in which drones fly around a bridge to read sensors designed to provide early warnings to problems.

"There is a huge need for better bridge-inspection techniques," the site quotes Tufts' professor Babak Moaveni as saying.

California transportation officials looked into using drones in 2008, but dropped the idea. Their report said: "Due to a number of implementation issues, the device did not perform as expected within the initial or extended schedule of events and was not deployed."

Among problems Zink sees for drones are startup costs and difficulty meeting Federal Aviation Administration rules, which federal officials say are due to be relaxed.