The route was designated along the Jefferson Highway, an auto trail that ran from New Orleans to Winnipeg.

While the route was signed concurrently, the SR 2 designation was removed in the 1955 Louisiana Highway renumbering.

[3][4] Route 3 remained co-signed with its U.S. counterparts until the 1955 Louisiana Highway renumbering, which eliminated such overlaps.

[5] Louisiana State Route 3-D ran 8.72 miles (14.03 km) in a north–south direction from US 65/SR 3 north of Lake Providence to US 65/SR 3 at Millikin.

While the route was signed concurrently, the SR 4 designation was removed in the 1955 Louisiana Highway renumbering.

In 1934, US 84 was extended on top of the eastern half of SR 6 from the Mississippi state line to Clarence.

While the route was marked concurrently, the SR 7 designation was cancelled in favor of US 190 in the 1955 renumbering.

Louisiana State Route 12 ran 84.3 miles (135.7 km) in a general north–south direction from Creston to Homer.

Louisiana State Route 15 ran 110.4 miles (177.7 km) in a north–south direction from US 65/US 84/SR 6 in Ferriday to SR 11 in Farmersville.

Louisiana State Route 15-D ran 3.4 miles (5.5 km) in a south–north direction from US 65/SR 16 near Red Gum to US 65/SR 3 in Clayton.

Louisiana State Route 19 ran 69.1 miles (111.2 km) in an east–west direction from Colfax to Harrisonburg.

Louisiana State Route 20 ran 128.8 miles (207.3 km) in a south–north direction from Alexandria to Shreveport.

Louisiana State Route 23 ran 20.1 miles (32.3 km) in a north–south direction from US 167/SR 22 west of Ville Platte to a dead end at Gold Dust.

Louisiana State Route 26 ran in a north–south direction from Kaplan to SR 1 (now US 71) near Lecompte.

SR 26 was extended south to Forked Island at the Gulf Intracoastal Waterway by 1928.

While the route was marked concurrently, SR 26 was deleted in favor of US 167 in the 1955 renumbering.

The route was part of the proposed Lakeshore Highway, but construction on the section from Kenner to Frenier was abandoned in the early 1930s mainly due to the completion of the Bonnet Carrè Spillway that split the route in half.

Louisiana State Route 35 ran in a west–east direction from Amite City to Franklinton.

Louisiana State Route 39 ran 41.9 miles (67.4 km) in a north–south direction from US 171/SR 42 in Leesville to SR 6 at Hagewood.

[2] Louisiana State Route 42 ran 194.8 miles (313.5 km) in a north–south direction from Cameron to SR 9/US 84 at Mansfield.

Louisiana State Route 43 ran in a general west–east direction from Breaux Bridge to the Gulf Intracoastal Waterway.

In 1926, the route was extended to the Gulf Intracoastal Waterway south of Abbeville.

Louisiana State Route 44 ran 19.6 miles (31.5 km) in a north–south direction from US 80/SR 4 in Ruston to SR 15 southwest of Farmerville.

Louisiana State Route 50 ran 17.7 miles (28.5 km) in an east–west direction from Campti to Goldonna via Creston.