U.S. Highway 90 (US 90), one of the major east–west U.S. Highways in the Southern United States, runs through southern Louisiana for , serving Lake Charles, Lafayette, New Iberia, Morgan City, and New Orleans. Much of it west of Lafayette and east of New Orleans has been supplanted by Interstate 10 (I-10) for all but local traffic, but the section between Lafayette and New Orleans runs a good deal south of I-10.

The stretch between Lafayette and New Orleans is planned as a southern extension of I-49 and is signed as "future corridor I-49". This part of the highway is important to the offshore petroleum industry, as it connects the cities of Lafayette and New Orleans to the port cities along the coast. Most of US 90 from New Iberia to New Orleans that has not already been improved to Interstate grade, is mainly an expressway, excepting the towns traversed through, that can be easily upgraded to freeway standards. The freeway east of Morgan City, bypassing Houma to the north, was originally built as Louisiana Highway 3052 (LA 3052); US 90 was shifted to it from its former alignment (now LA 182) once it was completed.

US 90 replaced almost all of the Louisiana section of the San Diego–St. Augustine running Old Spanish Trail. It was also designated Louisiana Highway 2 (LA 2) until the 1955 renumbering. A long section of the old road, from Lafayette to northeast of Raceland, is now LA 182.

Route description

State line to Lafayette US 90 enters Louisiana at the Texas line over the Sabine River as part of I-10. Separating at exit 4 and running parallel on the north side of I-10 through Sulphur, before rejoining I-10 east of Westlake, crossing the Calcasieu River, and again splitting from I-10 at exit 31B (running on the south side of I-10) going through Lake Charles as Fruge, West 4th, then East 4th, before leaving town. In Iowa US 90 intersects with the southern terminus of US 165 continuing east through Lacassine, Welsh, Roanoke, Jennings, and Mermentau. East of Mermentau US 90 runs north of and parallel to a section of the Old Spanish Trail through Midland, Estherwood, and Crowley. In Crowley US 90 makes a north then east jog, bringing it close and parallel to I-10, passing through Rayne, Duson, Scott, and then into Lafayette.

Lafayette to Raceland From Lafayette, US 90 traverses a south-southeast course to Patterson, where the highway takes a more easterly direction to New Orleans. The section east (south) of Broussard, beginning east of Captain Cade road but west of LA 88, to just west of Patterson, has been improved to Interstate grade and completed in June 2011. These improvements include the completion of the overpasses at Coteau Road (LA 88), Jefferson Island Road (LA 675), Center street (LA 14), Avery Island road (LA 329), South Lewis Street (Parish Road 605), Weeks Island road (LA 83), Darnall Road (Parish Road 211), Patout Road (LA 85), and Canal Street (LA 668). This section ties into the already completed section that begins at LA 318 and terminates at East Main street (LA 182) just east of Calumet. West of Berwick US 90 is listed as Interstate grade with a per hour speed limit from (mile marker 174) to east of Raceland and an intersection with LA 1 (mile marker 215B), before reverting to a standard divided highway and continuing on a north/northeast direction to New Orleans.

New Orleans US 90 enters Jefferson Parish, and after passing Avondale, heads north at an intersection with US 90 Business, called the Westbank Expressway, through Bridge City, and across the Mississippi River over the Huey P. Long Bridge. Crossing the river US 90, designated as S. Clearview Parkway, intersects with and runs east as the Jefferson Highway, that was originally part of the "Interstate Trail" and the "Pine to Palm" highway, a north–south transcontinental U.S interstate highway running from New Orleans to Winnipeg, Manitoba, Canada The highway terminus was at the corner of St. Charles Avenue and Common Street with a monument that was erected in 1916. The original highway was changed to follow US 90 and LA 48. After 1935 Jefferson became S. Claiborne Avenue at the Orleans Parish line and makes a sweeping south-to-north semicircle weaving through New Orleans. As the highway swings north it intersects and runs under an elevated I-10, where it turns northwest along Tulane Avenue. The highway soon turns northeast along South Broad Avenue—North Broad Avenue after the intersection with Canal Street—then runs into a pair of regular individual streets (i.e., not a street that has a median—or neutral ground in the vernacular of New Orleans—separating half of the lanes from the other half) that are from the old street grid and thus parallel at about from each other (named New Orleans Street & Allen Street) for about , crossing I-610 in this tiny span, and finally turning right (east) onto Gentilly Boulevard (which has a median), which eventually becomes Chef Menteur Highway (a mainly straight highway that replaced what is now called Old Gentilly Road), then crossing I-510, and then a few miles later, loses the median and meanders (i.e., in a manner similar to the way that Old Gentily meanders) until first reaching the national southern terminus of U.S. 11, which leads to the Irish Bayou community, and then passing the Venetian Isles community (a subdivision in which homes have a canal in the backyard for easy access to the surrounding lakes), and finally becoming a two-lane highway at the bridge over the Chef Menteur Pass to go past the Lake Catherine community until reaching the bridge over the Rigolets, after which US 90 finally leaves the corporate limit of New Orleans, entering St. Tammany Parish. The stretch in the Lake Catherine community is where Jayne Mansfield was killed in a car accident on her way to New Orleans from Mississippi.

In St. Tammany Parish, US 90 then enters Slidell. After exiting Slidell it heads east and crosses the Mississippi state line at a drawbridge at the Pearl River. The Jefferson Highway was the first north/south transcontinental highway in America, the second interstate highway, after the Lincoln Highway that it intersects in Colo, Iowa, but was the first international interstate highway in the world.

Interstates 49 and 910 The Business US 90 portion of the Pontchartrain Expressway is also designated as Interstate 910, however it is not signed as such. This is a temporary designation that overlaps all freeway portions of Business US 90 (the Pontchartrain Expressway, Crescent City Connection, and Westbank Expressway). When Interstate 49 is completed from Lafayette to New Orleans, Business US 90/Interstate 910 will be resigned as Interstate 49.

History

The modern US 90 has its roots in an early 20th-century auto trail known as the Old Spanish Trail, which was designated as State Route 2 within Louisiana when the state first numbered its highway system in 1921. US 90 was applied to the route when the numbered U.S. Highway system was implemented in 1926. With minor exceptions, Route 2 generally remained co-signed with US 90 throughout the state until such overlapping between U.S. and state routes was eliminated in the 1955 Louisiana Highway renumbering. Prior to 1955, as US 90 was gradually relocated onto newer and improved alignments, Route 2 was often moved accordingly. Former alignments remaining in the state highway system were then designated as part of State Route 1092, with shorter pieces designated as Route 2-D, 2-E, and so on as needed.

In Calcasieu Parish, on the border with Orange, Texas, US 90 originally crossed the Sabine River eastward into East Orange, Louisiana, a town consisting primarily of gambling, showboats, and supper clubs. The bridge over the Sabine River was removed after US 90 had been rerouted northward in Orange onto Simmons Drive and Interstate 10. In Lake Charles, US 90 traveled from Westlake down present-day Mike Hooks Road to cross the Calcasieu River on a bridge built in 1916. The road then traveled along Shell Beach and Lakeshore Drive to continue eastward on Broad Street. This alignment changed with the completion of the Lake Charles I-10 Bridge in 1952. In St. Charles Parish and Lafourche Parish, US 90 traveled down present-day LA 631, crossing the swing bridge still used by local traffic in Des Allemands. In Lafourche Parish, the old US 90 (now LA 182) splits off from the current US 90/Future I-49 just northeast of Raceland. Further southwest it enters Raceland, intersecting with LA 308, then immediately afterwards crosses Bayou Lafourche over a lift bridge. The route then goes to the right, through the middle of Raceland coaligned with LA 1 for a few thousand feet. It then takes a turn to the southwest as Willow Street or Old Houma Road, interchanging with US 90/Future I-49. Just south of this interchange, it travels as a four-lane highway until the junction with Prospect Boulevard/LA 3087. Old Highway 90/LA 182 then heads to Bayou Blue and on to downtown Houma as a major two-lane highway. LA 653 was US 90's original route but was supplanted in the 1950s by its current route, what is now LA 182, and most of this original road has been abandoned. Jefferson Parish: 1926–1928: The original alignment of US 90 generally followed today's LA 18 through Jefferson Parish and crossed the Mississippi River into Orleans Parish (city of New Orleans) via the Jackson Avenue Ferry at Gretna. The exact routing was as follows: LA 18 (River Road) from the St. Charles Parish line eastbound to Avondale. The original road through the Avondale shipyards continued straight along the river levee and no longer exists. LA 541 (continuation of River Road) and Bridge City Avenue through Bridge City. LA 18 (Seven Oaks Boulevard, formerly Bridge City Avenue) to Westwego. LA 541 (River Road), Sala Avenue, and LA 18 (Fourth Street) through Westwego. LA 18 (Fourth Street, Barataria Boulevard, and continuation of Fourth Street) to Gretna. Huey P. Long Avenue to the Gretna Ferry landing. 1928–1930: US 90 was re-routed over the Walnut Street Ferry in September 1928, shortening the route in Jefferson Parish to the former ferry landing at River Road and Sala Avenue in Westwego. 1930–1937: US 90 was restored to its original route through Jefferson Parish in May 1930, after widening and resurfacing of the Westwego-Gretna section was completed in April. 1937–1941: The Huey P. Long Bridge was opened in December 1935. US 90 was re-routed over the bridge, following Jefferson Highway into Orleans Parish, after widening of that thoroughfare to four lanes was completed in 1937. (LA 2 remained on the old alignment until the 1955 renumbering of Louisiana highways.) 1941–present: The current alignment (the "Boutte Cutoff") west of the Huey P. Long Bridge was opened in April 1941, bypassing the winding river road. This alignment was widened to four lanes in 1953. Orleans Parish (west of Peoples Avenue): 1926–1928: US 90 originally followed this route through New Orleans, starting from the Jackson Avenue Ferry landing: Jackson Avenue and South Claiborne Avenue to downtown New Orleans. Canal Street, North Broad Avenue, Bruxelles Street, and Gentilly Boulevard to Peoples Avenue. The above route, though signed in the field, had several problems that were mostly alleviated by a re-routing in 1928: The New Basin Canal bridge on South Claiborne Avenue had been closed in 1923 due to safety concerns. A temporary bridge was opened in July 1928, but it was a traffic bottleneck. Bruxelles Street became a one-way street in 1926, forcing westbound traffic to follow the unpaved Paris and St. Bernard Avenues from Gentilly to Broad. Jackson Avenue was also unpaved beyond St. Charles Avenue and did not connect directly to South Claiborne Avenue westbound. The Jackson Avenue Ferry service was considered to be inferior to that of the Walnut Street Ferry which the Old Spanish Trail had followed for years.