Louisiana State Route 20

Louisiana Highway 1
Route of LA 1 highlighted in red
Route information
Maintained by Louisiana DOTD
Length:	431.877 mi (695.039 km)
Existed:	1955 renumbering – present
Tourist routes:	National Scenic Byway: Great River Road Louisiana Scenic Byways: Boom or Bust Byway Cane River National Heritage Trail Wetlands Cultural Byway
Major junctions
South end:	Dead end at Bayou Rigaud in Grand Isle
	US 90 in Raceland I-10 in Port Allen US 190 west of Baton Rouge I-49 / US 167 in Alexandria US 71 / US 165 in Alexandria I-49 in Boyce US 84 / US 371 west of Coushatta I-20 / US 71 in Shreveport I-220 in Shreveport I-49 north of Shreveport
North end:	SH 77 at Texas state line northwest of Rodessa
Location
Parishes:	Jefferson, Lafourche, Assumption, Ascension, Iberville, West Baton Rouge, Pointe Coupee, Avoyelles, Rapides, , Red River, Caddo
Highway system
Louisiana Highway System Interstate US State Scenic ← LA 3286 LA 2 →

Louisiana Highway 1 Business
Location:	Natchitoches
Length:	4.8 mi (7.7 km)
Existed:	1975–present

Louisiana Highway 1 Business
Location:	New Roads
Length:	4.9 mi (7.9 km)
Existed:	2010–present

Louisiana Highway 1 (LA 1) is a state highway in Louisiana. At 431.88 miles (695.04 km), it is the longest numbered highway of any class in Louisiana. It runs diagonally across the state, connecting the oil and gas fields near the island of Grand Isle with the northwest corner of the state, north of Shreveport.

The part south of U.S. Highway 90 near Raceland is Corridor 44, a National Highway System High Priority Corridor. From Alexandria to Shreveport, the LA 1 corridor was used for Interstate 49.

Between New Roads, Louisiana, and the interchange with Interstate 49 at Alexandria, Louisiana, LA 10 forms part of the Zachary Taylor Parkway.

The southern terminus of LA 1 (29°15′37″N 89°57′49″W / 29.2603°N 89.9637°W / 29.2603; -89.9637) is at a dead end in Grand Isle on the south bank of Bayou Rigaud. It heads southwest and west through Grand Isle, turning northwest where it meets LA 3090 (the road to Port Fourchon). At Leeville the road crosses Bayou Lafourche on the Leeville Bridge and begins to parallel the bayou on its west bank, heading through towns such as Golden Meadow, Larose, Lockport, Raceland, Thibodaux, Napoleonville and Paincourtville. At Donaldsonville, where the bayou meets the Mississippi River, LA 1 turns northwest to parallel the river. (Southeast of Donaldsonville, LA 18 and LA 3089/LA 3127 parallel the Mississippi.)