History of the Seven Mile Bridge
The Seven Mile Bridge is the longest bridge among others that connect the Keys, and is part of U.S. Route 1 and the Overseas Highway. This bridge connects Knight’s Key (part of the city of Marathon, Florida) located in the Middle Keys to Little Duck Key in the Lower Keys. The history of the bridge begins in 1909 and includes an additional modern bridge that was opened in 1982.
The Seven Mile Bridge is 6.765 miles long and 38 feet wide, with a clearance of 65 feet. The design used with precast concrete, as a segmented box girder bridge. The main beams are made up of girders shaped into a hollow box.
Currently, there are two bridges, an older and a modern version. The older bridge was constructed from 1909-1912 as part of the Florida East Coast Railway and known as the Overseas Railroad or Knights Key-Pigeon Key-Moser Channel-Pacet Channel Bridge. In 1935, the Labor Day Hurricane damaged the railroad and the railway was sold to the U.S. government which restored it for vehicle use.
Restoration and New Construction
Old railroad tracks were recycled and painted white to be used as guardrails, and unsupported sections were added to make it wider for vehicular traffic. A swing span or movable bridge was used to allow for the passage of boats of the Intracoastal Waterway where the bridge crosses Pigeon Key. Unfortunately, more damage was caused by Hurricane Donna years later in 1960.
The swing span from the original bridge was removed and the section to Pigeon Key (2.2 miles), was closed in 2008 to motorized traffic when unsupported sections began to sag and now only used as a fishing pier and for pedestrians. The modern bridge was constructed between 1978 and opened for vehicular traffic in 1982. In 2014, a $77 million plan was approved by the Florida Department of Transportation to restore the old bridge with extensive repairs estimated to be completed by 2021.
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