Four years ago this week, the Minneapolis I-35W bridge collapse killed 13 people and injured 145. More recently, more than one in four U.S. bridges were found to be either structurally deficient or functionally obsolete, according to a 2009 study by the U.S. Society of Civil Engineers.

Visual inspection is still the go-to method of judging a bridge’s integrity. But researchers have been working on sensor arrays that could reveal problems long before a roadway is on the brink.

For example, University of Maryland electrical engineering researcher Mehdi Kalantari is designing a wireless early warning system made up of tiny sensors that can monitor a bridge's structural integrity and transmit that data to a central computer for analysis.

Kalantari's sensors are less than five millimeters thick and sense and measure structural parameters, communicate data and harvest energy from ambient light and ambient radio waves. The sensors are designed to be affordable: an average-sized highway bridge would need about 500 sensors costing a total of about $10,000. Such systems could help avoid catastrophes that cost far more than prevention.

—Larry Greenemeier

[The above text is a transcript of this podcast.]