From the south, LA 78 begins at an intersection with US 190 and LA 411 in Livonia. US 190 connects to Baton Rouge on the east and Opelousas on the west, while LA 411 heads southward along Bayou Grosse Tete toward Maringouin. LA 78 proceeds to the north, acting as the main north–south thoroughfare of Livonia. After a short distance, it curves to the northeast and continues through a largely residential area. later, LA 78 exits Livonia and turns further toward the east into an area known as Frisco. In Frisco, LA 78 curves to the north to cross a bridge over Bayou Grosse Tete. Immediately afterward, it intersects LA 979, a short connector to the nearby LA 978. From this intersection, LA 78 turns to the northwest and quickly begins a long curve back to the northeast through an area of mixed rural and residential development. later, the route reaches its end at LA 1 in Parlange, located on the west bank of the False River. LA 1 connects to Baton Rouge via US 190 to the southeast and follows the False River northward into New Roads. The route is classified as a rural major collector by the Louisiana Department of Transportation and Development. Average daily traffic volume in 2013 is reported as 4,200 within Livonia; 4,100 between Livonia and LA 979; and 3,500 from there to LA 1. The posted speed limit is initially in Livonia, increasing to at Bergeron Street. Upon reaching LA 979, the speed limit returns to, increasing to and finally to north of Frisco. LA 78 is an undivided, two-lane highway for its entire length.
History
Pre-1955 route numbering
In the original Louisiana Highway system in use between 1921 and 1955, the modern LA 136 was designated as State Route 136. Route 136 was created in 1928 by an act of the state legislature. At the time, US 190 had not yet been constructed through the area. Livonia was located just north of the junction of Route 1 and Route 7. These were the main highways connecting Baton Rouge with Alexandria and Opelousas, respectively. US 71 had been designated in 1926 and duplicated Route 1 through central Louisiana. Route 136 began at US 71/State Route 1 and proceeded east across Bayou Grosse Tete on Bridge Road. It then turned north to follow the present route of LA 78 to Parlange, where Route 93 continued toward New Roads. In 1933, a new highway was constructed along the New Orleans, Texas and Mexico Railway through Livonia, essentially replacing Route 7 between Baton Rouge and Krotz Springs. Two years later, this became part of US 190, which was extended from its original western terminus in Baton Rouge. Sometime before the 1955 Louisiana Highway renumbering, Route 136 was re-routed to begin at US 190 and proceed north through Livonia. This section of the route was formerly part of Route 981, which followed the present LA 411 along the east bank of Bayou Grosse Tete.
Post-1955 route history
LA 78 was created in 1955 as a direct renumbering of State Route 136. Its route has remained the same to the present day.
