<P> On January 21, 1970 the USS Yancey (AKA - 93), a United States Navy attack cargo ship carrying 250 people, was at anchor near the bridge tunnel . During a gale with winds gusting in excess of 50 miles per hour (80 km / h), the Yancey dragged her anchors and hit the bridge stern first, knocking out a 375 foot (114 m) segment of trestle . There were no vehicles on the bridge at the time of the impact, and no one was injured during the incident . During the 42 days it took to replace the damaged span the Navy offered a free shuttle service for commuters using helicopters and LCUs . </P> <P> In 1972, the bridge was again impacted by a barge which had broken loose, again closing the bridge - tunnel for two weeks while the span was repaired . </P> <P> The bridge - tunnel is frequently impacted by barges moving through the highly trafficked area; most incidents cause no damage and require a closure of the system for inspections before reopening . The most recent example of this was the September 2011 barge strike, which closed the bridge - tunnel for less than four hours . </P>

When was the chesapeake bay tunnel bridge built