Satellite images reveal which bridges around the world are at highest risk of collapse

Long-span bridges in North America face the highest risks of structural damage in the world, followed by those in Africa, according to a Nasa satellite study that could lead to a new way of preserving civilian infrastructure.

Bridges are some of the most vulnerable components of transportation networks that are regularly impacted by natural hazards.

Currently, regional authorities across the globe regularly inspect bridges visually to monitor their structural vulnerability, but such in-person inspections are often subjective and may miss some key early signs of deterioration.

Fewer than 1 in 5 bridges of lengths spanning 150m (492ft) or more have systems installed to track structural changes, scientists say.

In recent times, advanced satellites using radar imaging are giving scientists a powerful new way to watch over the world’s bridges.

A type of radar called Synthetic Aperture Radar can reveal structural displacements as small as a few millimetres and signal early structural problems long before inspectors notice them, say researchers from the University of Houston.

Now, a global analysis of 744 bridges reveals that bridges in North America, which were mostly built in the 1960s, are in the poorest condition, followed by those in Africa.

Some of the bridges referenced in the study include the Verrazzano-Narrows Bridge in New York City, the Vincent Thomas Bridge in Los Angeles, the Sunshine Skyway Bridge in Florida, the Humber Bridge in the UK, and the Matadi Bridge over the Congo River.

A large number of bridges in the US and Canada are currently approaching or exceeding their original design lifespans, according to the study published in the journal Nature Communications.

“Our research shows that space-borne radar monitoring could provide regular oversight for more than 60 per cent of the world’s long-span bridges,” said Pietro Milillo, an author of the study from the University of Houston.

“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,” Dr Milillo said.

The new technique, according to scientists, could enable more frequent deformation measurements across the entire bridge infrastructure network, unlike traditional methods, which typically occur only a few times per year and require personnel on the ground.

“Our work provides the global-scale evidence showing this is a viable and effective tool that can be deployed now,” said Dominika Malinowska, another author of the study from Delft University of Technology (TU Delft).

Scientists hope the method could be advanced further using data from the recently-launched Nisar satellite jointly operated by Nasa and the Indian Space Research Organisation (Isro).

Nisar is expected to gather imagery of nearly every bridge in the world twice every 12 days, and could make it possible to identify and track subtle changesIt could also be used to monitor other infrastructure, such as dams, railways, buildings, and levees, researchers say.