The Huey P. Long Bridge, Louisiana

Рет қаралды 1,968

Күн бұрын

The Huey P. Long Bridge, located in Jefferson Parish, Louisiana, is a cantilevered steel through-truss bridge that carries a two-track railroad line over the Mississippi River at mile 106.1, with three lanes of US 90 on each side of the central tracks. It is several kilometers upriver from the city of New Orleans. The East Bank entrance is at Elmwood, Louisiana, and the West Bank at Bridge City.
Opened in December 1935, the bridge was named for the late Governor Huey P. Long, who was assassinated on September 8 of that year. The bridge was the first Mississippi River span built in Louisiana and the 29th along the length of the river. It was designed by Polish-American engineer Ralph Modjeski and is designated as a National Historic Civil Engineering Landmark by the American Society of Civil Engineers.
On June 16, 2013, a $1.2 billion widening project by the Louisiana Department of Transportation and Development was completed and opened to motorists. The bridge now consists of three 11-foot (3.4 m) lanes in each direction, with inside and outside shoulders. Prior to the expansion, there were two 9-foot (2.7 m) lanes in each direction with no shoulders. In both cases, the road lanes flanked the twin railroad tracks contained within the truss.
The widest clear span is 790 feet (240 m) long while each of the three additional spans are 530 feet (160 m) long, making the total river crossing about 2,400 feet (730 m) long. There are three navigation channels below the bridge, the widest being 750 feet (230 m). The vertical clearance below the structure is 152.9 feet (46.6 m). The distinctive rail structure is 22,996 feet (7,009 m) long and extends as rail viaducts well into the city on both sides of the river from the central spans. It has sometimes been described as the longest rail bridge in the US, but the nearby Norfolk Southern Lake Pontchartrain Bridge, at 5.8 miles (9.3 km), is considerably longer. The highway structure is 8,076 feet (2,462 m) long with steep grades on both sides. As originally constructed, each roadway deck was 18 feet (5.5 m) wide, with two 9-foot (2.7 m) lanes; but because of the railroad component, it is unusually flat. Normally, bridges its height have a hump, but this bridge was designed flat to facilitate rail traffic.
The bridge is a favorite railfan location. It is owned by the New Orleans Public Belt Railroad, which is owned by the City of New Orleans and managed by the Public Belt Railroad Commission. The bridge was hated by many drivers in the New Orleans area due to the narrow 9-foot-wide (2.7 m) lanes without shoulders before it was widened. Additionally, where the East Bank approach met the superstructure of the bridge, the two vehicular roadways "jogged" or shifted inwards towards the bridge centerline about 1+1⁄2 feet (0.46 m) since the through-truss portion of the superstructure was 3 feet (0.91 m) wider than the deck truss portion of the east approach.
The foundation of the bridge is also unique. The land in and around New Orleans was formed by silt deposits brought down the Mississippi River. The clay topsoil, known colloquially as "gumbo soil," is compressible and unsuitable for foundation loads. As bedrock is around 1,000 feet (300 m) below the surface, making it too deep for normal bridge foundation construction, the main piers are seated on a layer of fine sand 160 to 170 feet (49 to 52 m) below Mean Gulf Level and rely on their size and mass to hold them in place.