Manchac Swamp Bridge

{{Short description|Bridge in Louisiana, US}}

{{Use American English|date=January 2025}}

{{Use mdy dates|date=March 2022}}

{{Infobox Bridge

|bridge_name= Manchac Swamp Bridge

|image=Manchac Bridge.jpg

|caption=

|official_name=

|also_known_as= I-55 Manchac Swamp Crossing

|carries= {{jct|state=LA|I|55|US|51}}

|crosses= Manchac Swamp

|locale= St. John the Baptist Parish / Tangipahoa Parish, Louisiana, USA

|maint= LA DOTD

|id=

|design=

|mainspan=

|length= {{convert|22.8|mi|km}}

|width= {{convert|95|m|ft|order=flip|}}

|height=

|clearance=

|below=

|traffic=

|open= 1979{{cite book |title=Preliminary Design of Bridges for Architects and Engineers |last=Melaragno |first=Michele G. |year=1998 |publisher=CRC Press |isbn=978-0-8247-0184-0 |page=377 |url=https://books.google.com/books?id=EGfxR4_TEUAC&dq=Manchac+bridge+interstate&pg=PA377 |accessdate=June 20, 2010}}

|closed=

|toll=

|map_cue=

|map_image=

|map_text=

|map_width=

|coordinates = {{coord|30.302946|-90.405807|scale:100000|display=inline,title}}

}}

The Manchac Swamp Bridge is a twin concrete trestle bridge near Manchac in the U.S. state of Louisiana. It carries Interstate 55 and U.S. Route 51 over the Manchac Swamp in Louisiana and represents a third of the highway's approximately {{convert|66|mi|km}} in Louisiana.

With a total length of {{convert|22.80|mi|km}},{{Cite web |title=Manchac Swamp Bridge |url=http://www.atlasobscura.com/places/manchac-swamp-bridge-2 |access-date=May 2, 2019 |website=Atlas Obscura |language=en}}{{Cite web |title=Manchac Swamp Bridge, one of the longest bridges in the world over water |url=https://www.dangerousroads.org/north-america/usa/6568-manchac-swamp-bridge.html |access-date=March 7, 2022 |website=www.dangerousroads.org |language=en-gb}} it is one of the longest bridges in the world over water, and is the longest bridge on the Interstate Highway System, and some claim it is the longest toll-free road bridge in the world.{{Cite web |date=August 1, 2017 |title=Longest Bridges in North America |url=https://www.worldatlas.com/articles/longest-bridges-in-north-america.html |access-date=March 7, 2022 |website=WorldAtlas |language=en-US}}

Opened in 1979, with piles driven {{convert|250|ft|m}} beneath the swamp, it cost $7 million per mile ({{convert|7|e6$/mi|e6$/km|abbr=unit|disp=output number only}}/km), equivalent to ${{formatprice|{{inflation|US-GDP|7000000|1979}}}} per mile ({{convert|{{inflation|US-GDP|7|1979}}|e6$/mi|e6$/km|abbr=off|disp=output number only}}/km) in {{inflation/year|US-GDP}},{{inflation/fn|US-GDP}} to construct.{{cite news |last=Loh |first=Jules |date=June 8, 1977 |title=Louisiana 'oasis' is cypress-paneled |page=6 |newspaper=The Tuscaloosa News |location=Tuscaloosa, Alabama |url=https://news.google.com/newspapers?id=WggdAAAAIBAJ&sjid=_Z0EAAAAIBAJ&dq=manchac%20bridge&pg=6767%2C1496622 |accessdate=July 20, 2010}}