When it comes to inspecting bridge decks, the method you choose doesn’t just affect the data quality—it significantly impacts cost, traffic disruption, and worker safety. Let’s break down the economics of three common approaches: conventional chain drag with lane closures, vehicle-mounted Ground Penetrating Radar (GPR) and Infrared Thermography (IRT) with rolling closures, and the new kid on the block—Unmanned Aerial Systems (UAS) using Infrared Thermography.
Baseline Assumption
- An average bridge deck size of 17,000 sq ft is used as our basis for comparison.
- MPT averages $10,000 per bridge deck of average sq ft.
- Rolling closure MPT averages $4000 per bridge deck of average sq ft.
1. Chain Drag with Full or Partial Lane Closures
- Inspection Speed: ~6,000 sq ft per day (about 3 days per bridge)
- Labor & Equipment Cost: ~$2,000/day
- Maintenance and Protection of Traffic (MPT): $8,000–$12,000 total (flaggers, signs, lane closures)
- Total Cost Estimate:
- $6,000 (labor/equipment over 3 days)
- $10,000 (avg. MPT)
- Total: $16,000 per bridge
- Cost per square foot: ~$0.94
2. Vehicle-Mounted GPR and/or IRT with Rolling Closures
- Inspection Speed: ~17,000 sq ft per day (1 bridge/day)
- Labor & Equipment Cost: ~$3,500/day
- MPT (rolling closures): ~$3,000–$5,000 (escorts, traffic control)
- Total Cost Estimate:
- $3,500 (labor/equipment)
- $4,000 (avg. MPT)
- Total: $7,500 per bridge
- Cost per square foot: ~$0.44
3. UAS with Infrared Thermography
- Inspection Speed: 3 bridges per day (~51,000 sq ft/day)
- Monthly System Lease: $6,000 → $300/day (based on 20 working days/month)
- Labor Cost: ~$1,200/day for a two-person crew
- MPT: None required
- Total Daily Operating Cost:
- $300 (system) + $1,200 (labor) = $1,500/day
- Per bridge: $500
- Cost per square foot: ~$0.03
The Bottom Line: Cost per Square Foot Comparison
| Method | Total Cost/Bridge | Cost per Sq Ft | MPT Required | Workers on Bridge? |
| Chain Drag | $16,000 | $0.94 | Yes | Yes |
| GPR/IRT Vehicle | $7,500 | $0.44 | Yes (rolling) | Yes |
| UAS with Infrared Thermography | $500 | $0.03 | No | No |
Conclusion: A Safer, Cheaper Future
UAS-based inspections using infrared thermography are rapidly proving their value—not only in cost savings but also in safety and efficiency. With zero lane closures, minimal disruption, and a cost per square foot that’s 30x less than chain drag, it’s a method that deserves a closer look—especially when you’re managing large inspection programs with limited budgets and potentially limited inspection seasons due to extreme weather.
