CASE C01 · US · 2016
MnDOT phased UAS bridge inspection research on 39 bridges, including the Blatnik Bridge
MnDOT trialled inspection drones on 39 bridges in phases from 2015 to 2017. It reported an average 40% cost saving, and on the Blatnik Bridge cost fell from about $59,000 to $20,000 and time from 8 to 5 days. One bridge cost more with the drone, and hands-on tasks and tight spaces remained beyond it.
| Owner | Minnesota Department of Transportation (MnDOT) |
| Provider | — |
| Location | Duluth, Minnesota, United States (plus Nielsville, St. Paul and Stillwater) |
| Aircraft | senseFly albris (prototype inspection UAS); Flyability Elios tested in Phase 3 |
| Sensors | RGB still/video camera (90° tilt), thermal infrared, ultrasonic proximity sensors |
Before
Snooper trucks reaching below the deck with inspectors in buckets or on ropes, usually with lane closures.
With drones
A GNSS-independent inspection UAS photographed steel arch, truss and culvert elements and captured thermal imagery.
Outcomes
| Metric | Value | Basis |
|---|---|---|
| inspection cost (Blatnik Bridge) | about US$59,000 conventional (excluding mobilisation/travel) vs about US$20,000 with UAS | Reported |
| inspection duration (Blatnik Bridge) | 8 days with four snoopers and an 80-ft lift vs 5 days with UAS | Reported |
| safety / traffic | some lane closures curtailed or eliminated (not quantified) | Reported |
| average cost saving (Phase 1–2 research) | 40% on average; savings from avoided access ranged US$540–21,000 per bridge | Reported |
| bridge-by-bridge cost (12 bridges analysed) | e.g. Structure 62504: $3,660 → $1,020; Structure 27831: $2,580 → $540; but Structure 19538 cost more with UAS ($1,080 → $1,860) | Reported |
Caveats & limits
- Not every bridge was cheaper: on Structure 19538 the UAS-assisted inspection cost more than the traditional one, and cost analysis covered only 12 of 39 bridges.
- Drones cannot perform hands-on tasks such as cleaning, sounding, measuring or tactile testing, so they supplement rather than replace the inspector.
- The albris was not collision-tolerant enough for very tight spaces (box girders, small culverts); a caged drone was trialled next.
- Figures come from MnDOT's research summary of a phased pilot, not from a full programme rollout.
- Large drones could not enter some confined spaces, and operation still required substantial training and skill.
Sources
- MnDOT improves on award-winning use of drones for bridge inspectionMinnesota Department of Transportation Research Services Full text read
- Benefit: MnDOT UAS bridge inspections saved 40% on average (ITS Knowledge Resources 2019-B01369)U.S. DOT ITS Joint Program Office Full text read
- Cost: UAS-assisted vs traditional bridge inspection costs (ITS Knowledge Resources 2020-SC00448)U.S. DOT ITS Joint Program Office Full text read
Sources checked: 2026-10-22