The Main Street Bridge, officially the John T. Alsop Jr. Bridge and nicknamed the Blue Bridge, is a bridge crossing the St. Johns River in Jacksonville, Florida. It was the second bridge built across the river. It carries four lanes of traffic, and is signed as US 1/US 90 (SR 5/SR 10). A lift bridge, it opened in July 1941 at a cost of $1.5 million. In 1957 it was named after Mayor John T. Alsop Jr., but continues to be known, even on road signs, as the Main Street Bridge. It remains one of the most recognizable features of the Downtown Jacksonville skyline.

Construction of the Main Street Bridge began in 1938 at a cost of $1.5 million by the Mount Vernon Bridge Company. It was permitted by the War Department in 1936 prior to World War II. The Main Street Bridge took three years to be built and had a dedication ceremony on July 17, 1941. The bridge was built as a vertical lift bridge with use of trusses in order to lift up to accommodate ships passing underneath it. The official name of the bridge, John T. Alsop Jr. Bridge, was dedicated in 1957 to former mayor of Jacksonville John T. Alsop. The bridge carries traffic to and from San Marco, Southbank, Downtown Jacksonville and Interstate 95. In 2014 the Main Street Bridge underwent an $11 million renovation to upgrade metal barriers and patch sidewalks.

With other nearby bridges having been rebuilt as fixed spans by around the end of the 20th century, the Main Street Bridge is now the only remaining moveable bridge carrying automobile traffic across the St. Johns River in the Jacksonville area. Of the eight vehicle crossings in the region, four (Shands, Fuller Warren, Acosta and Main St.) had included movable spans when they initially opened.

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  A 1992 map of the Main Street Bridge (the east one)
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  Looking south from downtown along Main Street towards the Main Street Bridge
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  Looking south through the truss of the Main Street Bridge
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  With lift span raised
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  Illuminated at night: View from Hyatt Regency Hotel, with the Acosta Bridge visible in the background
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  Sidewalk view from the south

The bridge opens on demand except during restricted hours. Restricted hours are 7-8:30am and 4-6:30pm.

• Media related to Main Street Bridge (Jacksonville) at Wikimedia Commons