It is bannered in all four cardinal directions depending upon the part of the route.

Undivided, two lanes, and largely secluded for the first several miles, it heads eastward and intersects LA 3219 near the community of St. James.

Continuing eastward, the route crosses into St. John the Baptist Parish before a junction with LA 640 south of Edgard.

As LA 3127 crosses into St. Charles Parish, the highway turns toward the southeast.

The final 1.1 miles (1.8 km) of LA 3127 consist of a concurrency with I-310, beginning at Exit 10.