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.

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.

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 120 yards (110 m) from each other (named New Orleans Street & Allen Street) for about 1⁄4 mile (0.40 km), 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.

[5] 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.

After exiting Slidell it heads east and crosses the Mississippi state line at a drawbridge at the Pearl River.

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.

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.