On Saturday morning, police officers stopped and searched for a third day box trucks as they approached the George Washington Bridge, which links New Jersey with New York, as well as the Queens-Midtown Tunnel, the Holland Tunnel and the Verrazano-Narrows Bridge, connecting the boroughs of Staten Island and Brooklyn.

CNN: STORY HIGHLIGHTS

The bridge involved was described as a small aluminium construction box frame structure, which was about 5m (16ft) long.

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Dorgan also cited an in-depth study of the bridge's fatigue potential conducted from 2004 to 2007 that recommended two alternatives for the bridge's future -- to add steel plates to reinforce critical parts of the bridge or to conduct thorough inspections of the wells inside the box to determine whether there were cracks.

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