U.S. Route 90 in Louisiana

Highway in Louisiana

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 297.6 mile (479 km), 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 (LS 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.

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.

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 70 mile (113 km) 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.

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 2300 mile (3701 km) 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.

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.

In Louisiana, current plans call for parts of US 90 to be upgraded to Interstate Highway standards from Lafayette to just west of New Orleans and designated I 49. The stretch of US 90 to be upgraded to I 49 is listed under High Priority Corridor 37 and stretches from the West Bank Expressway (US 90 Business near Westwego) to just north of downtown Lafayette, where US 90 splits from US 167 (the two highways converge in downtown Lafayette). The stretch of US 167 from US 90 to I 10 will also be upgraded and included as part of I 49. As of March 2008, due to a $1 billion surplus in the Louisiana state budget, the legislature approved a bill which proposed capacity improvements on US 90 in the Lafayette area. US 167/US 90 is currently six lanes from I 10 in Lafayette to LA 182 and LA 96 in Broussard.

US 90 Bus. (90 X) runs mainly along the old alignment through downtown Lake Charles, while US 90 uses I 10 and the newer Fruge Street. US 90 Bus. (90 Y) is the old route through downtown Lafayette, mostly along LA 182. US 90 Bus. (90 W) is mostly the old route (LA 182) through and east of Morgan City. US 90 Bus. (90 Z) is more of a bypass than a business route in the New Orleans area, running along the Westbank Expressway. US 190 splits from US 90 east of Slidell, just west of the Mississippi state line. It heads west into Texas, staying north of US 90.