In the aftermath of the September 11 attacks, U.S. officials scrambled to secure other national landmarks that might become future targets. Chief among them: California's Golden Gate Bridge. Might terrorists try to destroy the passageway between San Francisco and Marin County, and if so, how widespread would the fallout be? To answer those questions, the Homeland Security Dept. turned to a small company called Inrix, which was recently spun out of Microsoft (MSFT) and uses GPS-enabled mobile phones and tracking devices installed on commercial vehicles to monitor traffic conditions.

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