Houston Daily

A University of Houston researcher, Pietro Milillo, has collaborated with an international team to assess the condition of 744 long-span bridges worldwide. Their findings, published in Nature Communications, indicate that North American bridges are in the poorest state, followed by those in Africa. The study highlights that many North American bridges were constructed during the 1960s and are now reaching or have surpassed their intended lifespan.

The research proposes a solution involving spaceborne monitoring using Synthetic Aperture Radar (SAR) technology. This method provides high-resolution imagery and broad coverage, enabling frequent assessment of bridge stability from space. According to Milillo, "Our research shows that spaceborne radar monitoring could provide regular oversight for more than 60 percent of the world’s long-span bridges."

Milillo added, "By integrating satellite data into risk frameworks, we can significantly lower the number of bridges classified as high-risk, especially in regions where installing traditional sensors is too costly." The study found that when spaceborne monitoring is included in assessments, one-third fewer bridges are categorized as high-risk. Additionally, half of the remaining high-risk structures could benefit from satellite-based observations.

The team used Multi-Temporal Interferometric Synthetic Aperture Radar (MT-InSAR), a remote sensing technique capable of detecting millimeter-scale movements caused by slow processes such as landslides or subsidence. Dominika Malinowska from Delft University of Technology and the University of Bath stated, “While using MT-InSAR to monitor bridges is well-established in academic circles, it has yet to be routinely adopted by the authorities and engineers responsible for them. Our work provides the global-scale evidence showing this is a viable and effective tool that can be deployed now.”

Traditional methods like visual inspections are often subjective and infrequent—typically occurring every two years—and may miss early signs of deterioration. Structural Health Monitoring (SHM) sensors offer another option but are currently installed on less than 20% of long-span bridges globally and mainly on newer structures or those already identified as concerns.

Milillo emphasized the benefits: “Remote sensing offers a complement to SHM sensors, can reduce maintenance costs, and can support visual inspections, particularly when direct access to a structure is challenging.” He also noted that MT-InSAR allows for more frequent deformation measurements across entire infrastructure networks compared to traditional inspections.

The researchers found that integrating data from persistent scatterers—stable points detected by MT-InSAR—into risk assessments improves accuracy by reducing uncertainty. This enables better prioritization for maintenance planning.

Their proposed approach combines information from both SHM sensors and satellites such as ESA’s Sentinel-1 or NASA’s NISAR mission into structural vulnerability scores for bridges. This combined system delivers more frequent updates than conventional inspections alone and leads to improved risk classification.

The study notes particular advantages for disadvantaged regions like Africa and Oceania where traditional structural monitoring is limited or absent.