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The CNN website reports on the SHM (Strucutral Helath Monitoring) system installed by Roctest on the I35W bridge in Minneapolis.

Three-hundred-twenty-three high-technology sensors dot the structure, spitting out a constant stream of data regularly analyzed by engineers at nearby University of Minnesota.
At a total cost of about $1 million including wire connections and power sources, the sensors don't eliminate the need for visual inspections, but they do provide an extra layer of maintenance security.
The sensors monitor corrosion, stress and the movement of the bridge from the constant traffic.
"The fiber-optic strain gauge technology is fairly cutting edge," said Phipps. "A tiny beam of light is used to measure very small differences in the movement of the bridge when vehicles pass over."

Sorry, no flashing red lights or alarms go off when the sensors register something unusual, Phipps said, chuckling.
If the fiber-optic sensors show changes in the bridge's movement, data analysts would order a visual inspection, said Phipps, perhaps heading off structural damage that might pose a threat to the people crossing overhead. Less sophisticated strain gauges made of eight-inch pieces of wire measure more specific changes in the bridge's movements.
"It's like going to the doctor's office and having tests done. If something comes up different, then the doctor takes a closer look."

Read Full Article and see Pictures [Source: CNN]