Louisiana State Route 33

U.S. Highway 51
Route of US 51 highlighted in red
Route information
Maintained by Louisiana DOTD
Length:	69.116 mi (111.231 km)
Existed:	1926 – present
Tourist routes:	Louisiana Scenic Byway: Southern Swamps Byway
Major junctions
South end:	US 61 in LaPlace
	I-10 in LaPlace I-55 north of LaPlace LA 22 in Ponchatoula I-55 in Hammond US 190 in Hammond LA 16 in Amite City LA 10 north of Roseland
North end:	US 51 at Mississippi state line north of Kentwood
Location
Parishes:	St. John the Baptist, Tangipahoa
Highway system
United States Numbered Highway System List Special Divided Replaced Louisiana Highway System Interstate US State Scenic ← LA 50 LA 52 → ← SR 32 SR 33 SR 34 →

U.S. Highway 51 Business
Location:	Ponchatoula–Hammond
Length:	8.814 mi (14.185 km)
Existed:	1960–present

U.S. Highway 51 (US 51) is a part of the United States Numbered Highway System that spans 1,277 miles (2,055 km) from LaPlace, Louisiana to a point north of Hurley, Wisconsin. Within the state of Louisiana, the highway travels 69.12 miles (111.24 km) from the national southern terminus at US 61 in LaPlace to the Mississippi state line north of Kentwood.

After heading north through LaPlace to a junction with Interstate 10 (I-10) west of New Orleans, the highway joins I-55 on a 22-mile-long (35 km) twin-span viaduct across the Manchac Swamp. The bridge, which passes between Lakes Pontchartrain and Maurepas, is the second-longest bridge over water in the United States and serves as a vital hurricane evacuation route for the New Orleans metropolitan area.

With Ponchatoula served by the highway's only designated business route, US 51 splits from the interstate in the neighboring city of Hammond. For the remainder of its journey in southeastern Louisiana, the route closely parallels I-55, which carries the bulk of through traffic toward Jackson, Mississippi and points north. US 51 serves local traffic through a string of communities in Tangipahoa Parish situated along the Canadian National Railway line, including the towns of Independence, Amite City, and Kentwood.